An E6750 would be a wiser bang for the buck investment right now. The initial Penryn prices will be steep for at least 6 months, more likely a year. By Jan '09 you should be able to get a deal on a Quad Penryn.
Hanging on to the 7950gt is also a good move until they decide what DX10 is really gonna be. Also, SLi is much ado about nothing right now unless you are running a 30" or larger monitor. Very expensive way to get 20 more FPS.
Unless you are going 64bit OS, 2gb is plenty on the ram.