Originally Posted by prava;13880402
You are wrong here. Actually, 600W psu's are just useless, because they are on the middle of nowhere. On one hand, you can easily power any system that has only one GPU no matter the overclock you put into it with a 500W psu...and on the other hand, you will struggle with a high-end multi-gpu system. All in all: a suboptimal solution.
This is why is better to get 500-550W or 750+ W psu, because with the first ones you are perfect to power any single-gpu solution and the second one is much more adequate for power hungry multi-gpu solutions.
A quality 650W will run any two GPUs except HD2900XTs, GTX275s, GTX280s, GTX470s, GTX480s, and GTX580s.
GTX570s, HD6950s, HD6970s, GTX285s, etc are all fine in Crossfire/SLI.
This is assuming a highly overclocked Nehalems CPU; with a more power efficient CPU you could naturally run more.