Here a build i did for you. The only reason i chose the 750w psu is because it is on sale.
http://pcpartpicker.com/p/1guqC
Its not true about nividia cards being better. There some cards that are better than others. Its not like one card company is better than the other the whole time. The last generation nvidia cards were better when they first came out. But new drivers come out for amd and they made the cards perform better than the nvidia. Now the 7970 can beat the 680. The 7950 with a good overclock could even get to the same performance of a stock 7970.
The only real bonus to a nvidia card is physx and it performs better in some editing programs.
I would reccomend a tempest 410 instead of the source(which I have built with) the extra inch behind the motherboard and the cable routing options for a few bucks more is well worth it, especially if it is your first build.