Are you kidding? Whats the TDP of the 760? 95W? If you grabbed a mobo with onboard GPU you could use a 250W PSU. Why are you looking at 750s? Actually, if this is a pure folding/crunching machine this is a good idea. Mate it with a P55 board that has an IGP and buy a quality/high efficient PSU. 350W would be more then enough. That way this 24/7 machine doesn't chew up to much electricity.
If you're looking to SLI your 5870's, I would go with 750, or 850 if you can afford it. The XFX 750/850 are exceptional power supplies that go for much cheaper than the Corsair equivalent (both XFX's are modular). The 750w one is almost 70 dollars cheaper.
This is exactly why I had asked you to list your specs. You were being advised to get a 250/350/450/550 watt PSU for what turns out to be a 5870 CrossFire system. Oh! Well.
Point 1. 750 Watts is enough. You don't need 850. Especially a Corsair. I haven't checked, but both should have enough amperage on their +12V Rails (60-65, I'd assume) to run a system with the aforementioned configuration.
Point 2. For a 24/7 system, it makes a lot of sense to go with a gold rated PSU, rather than a silver/bronze. Especially at just 30 bucks extra. Better efficiency certainly won't hurt. The AX does it then, IMO.
They also state that it could have qualified for gold standard efficiency, but was just over spec so Corsair decided to market it as silver. Further, Hardwaresecrets was able to pull 900 W from the unit but points out that at that level the efficiency is "only" 83%, below 80+ gold standards.
Few minutes ago, I check at Newegg they now have Asus GTX 460 TOP 1GB. I will be playing SC2, Bad Company 2, Crysis and many others on my wish list. I think this video card would be better to do Folding@Home what you guys think I should go for. Yes, I'm going to SLI.