if I was going to upgrade, and i had what you have, i would get a board with PCI-e 3 on it. It’s already out, so it’s only a matter of time before all the fast gpu’s will need pci-e 3 to really perform to their potential.
if you can wait until april, intel has the Z77 chipset coming out which will have everything new you could possibly want and that will last you longer than anything you can buy today. (this is assuming you will want to keep playing new games as time goes by)
if you can’t wait, then there is the X79 chipset, which has PCI-e 3.0, but it’s expensive, and it can only do usb 3.0 with an add-on controller.
if you don’t want to switch to intel, and you can’t wait until AMD’s new chipset comes out (trinity), then I agree with the other posts, buy that new phenom chip, and get yourself more RAM. However, I don’t think you need to spend $$ on a new copy of win 7, and I think that your setup will only really need 4 GB of RAM before the RAM is not your problem anymore.
Win 7 is nice, but as long as you are not running into compatibly issues, that’s $$$ you don’t have to spend.
Also, you may want to invest in a modest SSD. I’ve seen the 128GB samsung 830 for $170 on some etailers, and you can always put that in your next rig when it’s time for a bigger upgrade.