1 - No
2 - Assuming there's no OC I'd say 650w would be fine.

I'm basing that assumption off of this article here on Tom's Hardware. Granted they are using a GTX 260 but they're measuring power "at the plug". So unless your 275 somehow manages to suck up a few hundred more watts I think you're good on a 650W PSU. But if I may suggest another manufacturer of PSUs which is PC Power & Cooling. I believe that PCP&P is the purest form of power man can buy.