Hi, I'm planning on building a computer from scratch and I was wondering if an Ultra LSP750 would be enough to run 2x ATI 5850's in crossfire and amd phenom ii x4 965 3.4ghz. I might be overclocking in the future.
AMD recommends 500W for a single 5850 and 750W for crossfire. So yes, that's fine. Unless you go really extreme on the overclock or run water cooling pumps (or a bajillion fans) 750W should be just fine. The question is, is it a quality PSU? That I do not know.
Those units are OK but are not really the best for your setup its really weak on the 12 volt rail at 45 amps for a 750 watt unit. If you already have the unit give it a try but if you looking to buy a new PSU and you are thinking of getting that unit don't.
Quality 750 watt units will usually have between 54 and 60 amps on the 12 volt rail compared to your 45 amps. I think that unit might have some problems running those cards.
Another problem is you need 4 6pin PCIE connectors to run 2 5850's that unit only has 2 I would recommend getting a new unit with more power on the 12 volt rail preferably above 50 amps on the 12 volt rail for crossfire with those cards.
Good point SAAIELLO I only considered the Wattage, my mistake. For crossfiring those cards you need 4 8-pin or 6+2 pin connectors and this PSU appears to have only 1 8 pin and 2 6 pin.
Tom's Hardware recommended a really good one that I ended up purchasing, the Corsair 750TX. It has 4 8 pins for PCIe as well as 60A 12V rails. I specifically got this one so I can crossfire 5850s down the road.