q8200s are a bit cheapers + 45nm for less power and less heat
True, but Q6600s are faster and overclock much better if you're going for that.
I need to keep the power low and GPUs would suck up a lot. Mabye I could put just one on each motherboard but then I would need a lot better PSU and it would use more power
I understand that, but what I'm saying is you need to take the overall power usage and crunching power of the farm into consideration. Sure, a Q8200, board and RAM suck less power than a Q8200 and a 9600GSO, however take the F@H performance into account and work out what combinations will give you the best performance for the least power.
Put another way (pulling numbers from the air, please do actually work these out) Q8200 = 1500ppd and 100W, Q8200 + 9600GSO = 3500ppd + 200W. The second is clearly a better choice, as it uses twice the power for over twice the points. I know it's not all about points, but as the work units vary so much I can't say how many units it will crunch per day so the points will have to indicate that.
As I say though, do check up on those numbers, I could be way off base and I'm just guessing.
At the minute, Nvidia does destroy ATI at F@H performance, but ATI are slowly catching up. What I hear is that the newer units (such as the 590x series, worth 1680 points each) benefit more from a larger amount of shaders and this trend will continue, bringing ATI cards' performance up. Nvidia has much better folding performance now, but ATI may have better performance in the future, so it's a trade-off.
The best bang for your buck was the 9600GSO/8800GS, but the lower number of shaders lowers their performance in the newer units. Also the newer 9600GSO is crippled, with only 64 vs 96 shaders for the older ones.
If you go the GPU route I'd recommend at least an 8800GT/9800GT. The 8800GTS/9800GTX give better performance and can actually be easier to find. Going higher and the GTX260 is a beast at F@H, but that might suck a bit too much juice for a farm.
