Looks like all you need is a new Mobo Ram and GPU. I think it would be pointless to upgrade the 940 when the hex cores are around the corner.
Also seeing how you are looking to spend 2-3 grand on a computer why dont you ready yourself for the hex cores from AMD?
Here check this out. I think this is all youll need.GIGABYTE GA-890GPA-UD3H AM3 AMD 890GX
$139 This board has both U3S6 and the new 890 chip set that is supposed to be optimized for the hex cores when they come out.G.SKILL Ripjaws Series 4GB (2 x 2GB) CL7 1600
HD5970 if you can find one in stock. 700 bucks.
Currently the 5970 is the best card on the market until Fermi comes out and from all the reviews Ive read it probably still will be.
I think upgrading would be your best choice.