I agree that your build will probably not require more than 750 Watts... i think the only way to surpass that is to have quad sli with the dual gpu cards or something.
However, when i was in your position, i found that the most reasonable price was a newegg brand Rosewille 1 Kilowatt PSU. At the time it cost around $120, its probably cheaper now. Yes its overkill, but if you count on the fact that PSU's lose 10% capacity every year, you don't want your psu to run out of juice after only 2-3 years. So check the prices, if its not much more expensive to bump up to a higher wattage, go ahead and get it. Yeah you lose 10 or 20 dollars, but you don't have to worry, which is worth it in my opinion. And let me point out, the Newegg brand stuff is much cheaper but probably just as good quality.
edit-- looks like prices are the same as 2 years ago... hehehe