First off, using an AMD video card with an AMD CPU makes no difference, at all!

As to the PCIe interface, very few of the new cards have a problem running on non 3.0, and you would not know the difference between 2.0, 2.1 or 3.0 when in game.

By the sound of it you have a PSU good enough to support any card (if it is of decent quality), so with your budget you could get a GTX 570 which is an awesome card for the price.

However, if you are currently hanging in there, I too would wait for black friday and see what is on sale, possibly we will know more about the new engine and how the different cards (series, model and AMD/Nvidia) runs it.