Should last 2 years or so. If not you can always add in more RAM and a newer video card or go crossfire. That CPU is a beast and the 6870 can run anything now at max depending on your resolution. It might have probs with Metro 2033 at 1920x1080 max detail but other than that it'll run anything smoothly. If you are planning to do Crossfire in the future I would recommend going with a 700 or 750W version, 2x 6870s eat up a lot of power.
Yes then get the build in my siggy.
But switch the CPU out for the i5 2400. Switch the GPU out for a 560 Ti. That'd add about 130$ to total to about $730. I assume you won't CF or OC. So you can change the motherboard to this motherboard instead to save money.