Video Card Advice

[Freakin]

You should be able to find a Geforce 8800GT for $300 or less. You JUST missed one like two days ago that was on sale at dell home for $208.

At this point I would not bother upgrading to anything besides an 8800 or better. You're going to want DX10 going forward, and a 8600 wouldn't cut it.

I'm a guy who always just buys about a $250 video card. When my games get too slow, I figure out what I can afford; if the next step up is going to make a huge difference, then I wait 2 months for it to be $250.

Paying $600 for video cards is insane, IMO. With your setup, the bottleneck is likely to be RAM. I doubt you are even hitting that bottleneck with a 6800. You will likely hit it with an 8800, but you should still get GREAT performance increases.