But for how long? You are one of THE GPU gurus I was referring to that knows these cards, Mac Pro limitations etc. Is it really possible to run this thing frequently maxed out without supplemental power?
I don't know the answer to this.
I used it with an external supply as I have one sitting next to my testing rig.
We'll find out as more people try I guess.
I can't advocate it as I don't want the responsibility of blowing up even 1 logic board due to my advice.
A foolish man in Germany had me mod a GTX580 lightning which required 2 @ 8 pins. Despite my entreaties to the contrary, he used it with 6 to 8 adapters.
Then he played games in Windows and OVERCLOCKED AND OVERVOLTED it. (Yes, I know...) He then wrote me a day later surprised that his machine was having significant issues, not only with 580 but also with his RAID card. I am 100% certain that he drew too much current through card, when it didn't get enough from the 6 pins, it drew it through the PCIE bus and burned a trace there, killing a power channel in his PCIE bus, which killed his RAID card. A mess.
So, it is possible to really screw things up. But he wasn't asking for it, he was BEGGING for it.
As with anything, YMMV, if your mac Pro is maxed out and in a hot room and has cards above and below each other, you have less headroom than someone with a single Quad core and no other cards.
The other point I can make is that I have a 3,1 and a 4,1 and the 3,1 will cut out much more quickly with Furmark at full screen than the 4,1 will.
The 3,1 will even crap out doing that test with a 570, which in theory should be OK. So, in my case, my 3,1 has less headroom than a newer 4,1. The older 4,1 was also crapping out quite a bit before slot totally fried running 580 with 6 to 8 pin. The reason I don't popint that story out more is that that machine had tested a few HUNDRED cards before dying, so slot may have had more wear than most. But sparks came out and SLOT 1 is now capped off.
To be safe & secure, use proper power.
If you enjoy living on the edge, use adapters and keep your fingers crossed. But I don't recommend it.