Ok first i need to know about what kind of budget or how much are you looking to pay.
What kind of games are you planning on playing and are you looking to upgrade in the future.
Those are the main 2 things i need to know but what i can tell you right now is that depending on what xfx 6950 you getting the max size they are is 10.2 inches and that case holds a 10.5 inch card from what i'm reading.
I can see that the 3.3v and 5v amps are listed at 25 and the 12v amps are listed at 16 amps which pretty much means the PSU is nothing but garbage.
Fifteen years ago that would have powered the average PSU, but those numbers should be reversed for PCs operating in 2011. At least for the Enlight Sniper 650w, they never got with that program.
That is 1 for 1 on the bad PSUs scale, so you are rolling the dice if you go with the Enlight EN-TOP 650w.
I commonly use the example that you wouldn't put a Dodge Neon engine in a Dodge Viper you were planning on driving, so don't do it with your PC either. It would be sad if you blew up a $300 video card because you only paid 50 cents for the PSU.