Well, you can get HD6870 and move that card when you build a new gaming machine in next 2 months...
Or if you want a not too expensive card then go with HD5850, that's much faster than HD4850 and i'm pretty sure you can maxed out everything with HD5850 at 1680x1050.
Seems like a no brainer, but since I'm only running at 1680x1050 would that not be overkill (not that thats bad..lol) My monitor is new so i wont be upgrading aytime soon there. Also wouldn't i require a new PSU?
An HD6850 is $180 and a better deal for the money than the HD6870, especially if you give it an overclock, and should be excellent for 1680x1050. It also only has one power connector not that it matters much as a 500w Earthwatts can handle any of the cards discussed in this thread.