Thanks for the suggestions. It is a 420 watts PSU. Right now I have it paired with a 5670 and Athlon x2 processor and seems to work perfectly when I play diablo. I don't know if that will change if I get the 6870. It seems like it will work but not sure.
In the above article, they built a computer that has similar power needs to your own, and they used an Antec Earthwatts 430. 650 watts would be complete overkill, since your proposed build won't be able to pull anywhere near that much even under full load.
And yes at 1440 x 900, a 6870 will be able to power even the latest games with at least good graphics settings. I have a 6870, and with lowering only the AA and AF a little, I was getting 30+ fps on Battlefield 3 using a 1920 x 1080 monitor.
Yeah everything should be compatible. The only thing you might need to consider is that the 6870 needs two auxiliary 6-pin power connectors from the power supply, and I think yours may only have one, so you'll need an adapter to get the other 6-pin connector.
Alright everyone I ordered the g850 Mobo combo, case, and the 8gb ram. Total came out to be $210 but with rebate will come down to $170. Still need to order the HDD, DVD drive, and graphics card. If anyone can find a good DVD drive/HDD combo please let me know.
8gb of ram over 4 isn't going to show hardly any performance increase in most applications, but ram is so cheap right now that there's no real reason not to get at least 8gb. As far as the longevity of the build, the biggest risk you have for being held back would be the G850, since it's a dual core. But most applications these days favor instructions per cycle instead of multiple cores, so even a dual shouldn't be that big of a deal for a year or two. And the Sandy Bridge architecture will be fast for a few years as well. So yeah, at least two good years of decent performance.