:/
You don't seem to understand. 3GHz to 3.4GHz doesn't make much of a different. If you take a C2D running at around 4GHz, then it is equivalent to an AthlonX2 running at around 5.4GHz or even more.
Why can't you overclock your current CPU? It will do 3.2GHz or if you are lucky 3.4GHz and that will be OK for your SLI setup. I mean, you will get more FPS if you have a faster CPU, but there is no difference between 60 fps and 80 fps to the human eye. Things only get BAD when the FPS you get is around 25 BECAUSE OF THE CPU, not the VGAs. In strategy games, such a Tiberium Wars, your CPU will run very slow, if you play a 8 player Brutal difficulty level skirmish challenge. In games such a Crysis where AI and Physics processing is high, the CPU might be a bottleneck, but NOT a lot.
And keep in mind that, you can't have Cross Fire on your motherboard. If you really need an upgrade to ATI, the only option you have is a HD 4870X2. Nothing less. But if you go nVidia's route, you have a lot of more options. (9800GX2 SLI, GTX280, GTX260SLI, GTX280SLI

)
BUT... if you really want to upgrade your graphics cards setup, I suggest you first buy a 24" monitor with 1920x1200, because at 1680x1050, 8800SLI setup is more than enough to play any game with max details, and I suppose even the games that are supposed to come in the next year or so will performance similarly.
P.S.
If you really wanna upgrade the CPU, try to find the new AthlonX2 6500+ which runs at 2.3GHz, but it is not widely available. It's a dual core Phenom CPU, and not sure if your mobo will support it. Some benchmark results looks VERY promising. Note that this is 2.3Ghz vs 3.0GHz, and you can OC it to around 3.4GHz for a 50% more performance. Then it is a very good CPU!!!
http://xtreview.com/addcomment-id-6272-view-Athlon-X2-6500-vs-Athlon-X2-6000.html
http://babelfish.yahoo.com/translat...797775d10042.html&lp=zt_en&btnTrUrl=Translate