I've got that TX750 PSU with two 1GB 560 TIs (900MHz) and a 2500k OC'd to 4.4GHz with no complaints.
There's no way it'll bottleneck it because I know a lot of people use stronger cards w/ the 2500k. When it comes to gaming the only real difference you'll see with that i7 is the 1/10 GHz. That and people with a "best buy" knowledge of processors will be more impressed when you throw around i7 instead of i5.
oh yeah... and I'd totally go with a stronger single card if I was dropping $500 at one time rather than accumulating hardware over time.
Gah, why would you recommend a Thermi 580 when the 7950 is better everywhere, and cheaper.
The 7950 overclocks like a god, draws less power than the 580, is cooler and quieter!
I never recommended the 7950 over the 580, it's always better to get a fast single card then sli/xfire with two weaker cards and the 580 and 7950 cost as much as as 2 560ti's. I would go with the 7950 over the 580 even though I'm disappointed in the 7900 series.