I am using 1pc of xfx 9800gtx extreme on Antec 650W.
If I got a second xfx 9800gtx extreme, could anyone suggest the current PSU is enough for 2 SLI (+ overclocking)?
If not how much do I need to upgrade? (e.g. 850W)

Or eventually I should directly go for 1000W?

Thanks for your opinion~