Great information. I just want to make absolutely sure that I understand everything!
Ok so first off I have a early 2009 Mac 4,1. I have Mountain Lion 10.8.2 installed.
The following is what I think I know, if I'm incorrect in any areas could you please let me know.
If I was to buy a GTX 670 or 680 they come with two 6 pin connectors. As long as I don't buy an overclocked version they will work out of the box without needing an external power supply. I'm assuming that the amount of vram they have doesn't affect the power, so a 2GB would be the same as a 4GB? I'm also assuming that they'll plug right into the existing cables that I have for my ATI card which is an HD 4870? - Yes, I believe so.
Mountain Lion drivers allow you to boot up with the GTX cards as in I'll see as boot screen (the Apple Logo)? No - You would need a Mac EFI for that and as far as I know no one has figured that one out yet. But, you will boot from a black screen then directly into the desktop. Note - MacVidCards does modify GTX570 and GTX580 cards with Mac EFI.
It will use PCIE 2 not 1, as long as I don't use windows? - Yes
Now for two questions I'm still not sure of.
1: Someone asked if you can display two monitors without an adapter but I didn't see an answer. I'm assuming you can? - I believe two monitors is the max on an Nvidia card.
2: If I've understood correctly, if you have a 2GB card or above, the card won't work at all so you still need to run the CL 2gb limit process with the latest drivers? - A card with >2GB Ram will work, you just won't have Open CL. You need to do the Open CL Fix for it to work properly.
Is it the same process as for 10.7.5? - As far as I know the answer is No.
Someone posted in this thread this great tutorial http://www.youtube.com/watch?v=u6pEmIiN4Co but it's for 10.7.5 so not sure if it will be the same for 10.8.2
Thanks again for your consistent support, it's really helped me out.
I have posted what I believe are the answers to your questions above. If I am incorrect, I'n sure the experts will correct me.
Lou