As promised, here are the pics, fitting comments and results of changing the stock 5870 cooler in my 2010 Mac Pro for something quieter and more effective. Yes, as anticipated it was a tight squeeze but no nasty surprises.
I have not included any close-ups of the cooler itself since plenty are available on the web. I am really just concentrating on the fit into the case and any issues along the way.
===
Arctic Cooler Accelero XTREME Plus with fitting kit VR001.
STRIP DOWN : After removing the stock 5870, I undid ALL the visible screws on the back side of the card (including those three tiny ones) and the two on the side. The cooler came off easily into two pieces - back-plate and fan assembly. I noted that thermal tape had adhered to the VRM chips.
CLEANING : Using Arctic Silver ArctiClean, I thoroughly cleaned the GPU, all memory chips, the VRM next to the GPU and the 6 VRM in that group in a line and set the card aside to dry. I also removed the supplied thermal compound from the new cooler as I had some Arctic Silver AS5 ready to use and I wanted to do a dry fitting to check the space in the case.
During the dry fitting, I noticed that although the card went in easily enough, it sagged a little and the underside made contact with the metal of the case. I decided to re-attach the backplate from the stock cooler to protect the underside of the card and to allow it to lock in place nicely with the PCI holder near the fan. Four small zip-ties securely fastened the backplate onto the bare card.
HEAT-SINKS : Since I would only be fitting this once and keeping the card for years, I discarded the Thermal Cement that came with the VR001 kit. It is supposed to be air-cured glue with some standard thermal compound mixed in. I bought some Arctic Silver Thermal Epoxy instead. This stuff is a PERMANENT adhesive.
I selected the heat-sinks from the VR001 kit, cleaned the undersides with the ArctiClean and set them aside.
The Thermal Cement cures very rapidly, going tacky and stiffening in under 5 minutes so I applied it in two batches. Firstly I applied the VRM heat-sinks - three large and one small. The Thermal Cement can be used very sparingly and extreme care must be taken not to get any over the edges of what are very small components. A suitable tool can be made from a wooden cocktail stick chopped in half and smoothed.
Once I had the VRMs covered, I mixed some more Thermal Cement and repeated the process with the 8 RAM heat-sinks, taking care to align them with the inner edge as shown on the cooler instructions.
The cement takes an hour to cure and I made sure to allow all this time as I didn't want to knock any of the VRM heat-sinks off.
The result...
COOLER : Fitting the cooler itself was trivial. I spread some of the Arctic Silver AS5 on the GPU, connected the PWM fan cable (don't forget this) and flipped the card over onto the cooler. There are just four screws and washers to secure everything. I placed the washers under the backplate carefully before fitting the screws. Tighten the screws in opposite pairs and that is it.
GETTING IT INTO THE CASE : I tucked the power cables out of the way and just lined the card up dead straight. With absolutely no scraping or twisting, it just slotted straight in. Yes, it was a VERY close fit, but it went in. To be honest, the only tricky part was making sure the backplate bracket went into the PCI card holder properly.
I latched the bar back across, put the PCI plate back with its thumb-screws and connected the two power leads. There was plenty of length in the power leads to pass over the larger cooler without fouling the fans.
The only tight fit was the clips on the power leads. The cooler heat-sink rests on them slightly.
Overall, the card now takes up three slots as advertised on the Arctic Cooling website.
RESULTS : I did not have any heavy-duty stress testers such as FurMark, so I made do with Warcraft in Orgrimmar at peak time with the details cranked up higher than I would normally play on so that the frame rate dropped below the 100fps cap.
AMBIENT : 23C
STOCK COOLER : Idle 38C, load 63C
Accelero XTREME Plus : Idle 27C, load 52C
I am well aware that the Arctic Silver AS5 will take quite some time to settle in before results are accurate. I also know that WoW doesn't really push the card but it is what I had available.
NOISE : I cannot hear the new cooler at all even under load, so all the Mac Pro does is run the case and CPU fans as they warm up. An excellent result!
VERDICT : A fairly straightforward cooler swap which has reduced temperatures and noise. Due to the use of Thermal Epoxy, I would not rate this for the faint hearted but if you are used to doing cooler swaps, it has no surprises.
I have not included any close-ups of the cooler itself since plenty are available on the web. I am really just concentrating on the fit into the case and any issues along the way.
===
Arctic Cooler Accelero XTREME Plus with fitting kit VR001.
STRIP DOWN : After removing the stock 5870, I undid ALL the visible screws on the back side of the card (including those three tiny ones) and the two on the side. The cooler came off easily into two pieces - back-plate and fan assembly. I noted that thermal tape had adhered to the VRM chips.
CLEANING : Using Arctic Silver ArctiClean, I thoroughly cleaned the GPU, all memory chips, the VRM next to the GPU and the 6 VRM in that group in a line and set the card aside to dry. I also removed the supplied thermal compound from the new cooler as I had some Arctic Silver AS5 ready to use and I wanted to do a dry fitting to check the space in the case.
During the dry fitting, I noticed that although the card went in easily enough, it sagged a little and the underside made contact with the metal of the case. I decided to re-attach the backplate from the stock cooler to protect the underside of the card and to allow it to lock in place nicely with the PCI holder near the fan. Four small zip-ties securely fastened the backplate onto the bare card.
HEAT-SINKS : Since I would only be fitting this once and keeping the card for years, I discarded the Thermal Cement that came with the VR001 kit. It is supposed to be air-cured glue with some standard thermal compound mixed in. I bought some Arctic Silver Thermal Epoxy instead. This stuff is a PERMANENT adhesive.
I selected the heat-sinks from the VR001 kit, cleaned the undersides with the ArctiClean and set them aside.
The Thermal Cement cures very rapidly, going tacky and stiffening in under 5 minutes so I applied it in two batches. Firstly I applied the VRM heat-sinks - three large and one small. The Thermal Cement can be used very sparingly and extreme care must be taken not to get any over the edges of what are very small components. A suitable tool can be made from a wooden cocktail stick chopped in half and smoothed.
Once I had the VRMs covered, I mixed some more Thermal Cement and repeated the process with the 8 RAM heat-sinks, taking care to align them with the inner edge as shown on the cooler instructions.
The cement takes an hour to cure and I made sure to allow all this time as I didn't want to knock any of the VRM heat-sinks off.
The result...

COOLER : Fitting the cooler itself was trivial. I spread some of the Arctic Silver AS5 on the GPU, connected the PWM fan cable (don't forget this) and flipped the card over onto the cooler. There are just four screws and washers to secure everything. I placed the washers under the backplate carefully before fitting the screws. Tighten the screws in opposite pairs and that is it.
GETTING IT INTO THE CASE : I tucked the power cables out of the way and just lined the card up dead straight. With absolutely no scraping or twisting, it just slotted straight in. Yes, it was a VERY close fit, but it went in. To be honest, the only tricky part was making sure the backplate bracket went into the PCI card holder properly.
I latched the bar back across, put the PCI plate back with its thumb-screws and connected the two power leads. There was plenty of length in the power leads to pass over the larger cooler without fouling the fans.
The only tight fit was the clips on the power leads. The cooler heat-sink rests on them slightly.

Overall, the card now takes up three slots as advertised on the Arctic Cooling website.

RESULTS : I did not have any heavy-duty stress testers such as FurMark, so I made do with Warcraft in Orgrimmar at peak time with the details cranked up higher than I would normally play on so that the frame rate dropped below the 100fps cap.
AMBIENT : 23C
STOCK COOLER : Idle 38C, load 63C
Accelero XTREME Plus : Idle 27C, load 52C
I am well aware that the Arctic Silver AS5 will take quite some time to settle in before results are accurate. I also know that WoW doesn't really push the card but it is what I had available.
NOISE : I cannot hear the new cooler at all even under load, so all the Mac Pro does is run the case and CPU fans as they warm up. An excellent result!
VERDICT : A fairly straightforward cooler swap which has reduced temperatures and noise. Due to the use of Thermal Epoxy, I would not rate this for the faint hearted but if you are used to doing cooler swaps, it has no surprises.