The E6700 will perform better than the 6000+ (the amount depends on the game), but costs more. For the GPU, it depends on the resolution you play at. If it's 1280x1024 it's not worth it. Leave the option open for later.
As far as Track's comment, the E6420 doesn't out perform the 6000+ to the best of my knowledge. He is right, your PSU will not cut it. I'm not sure about what to make of his comment on Corsair. He is either speaking from one experience or has seen so many bad chips of Corasir RAM that he won't bother with it. who knows.
Basically, at stock AMD is the best bang. When overclocker, C2D is.
If you get 650i, you don't need to o/c the ram. Just run it unlink/unsynched, & o/c the cpu. That said, you don't need expensive ram. Any brand name value ram at 533/667/800mhz will do. dual channel kits are preferred.
If I had the money, I'd take the e6700 hands down & o/c it to hell.
I would go with the C2D setup even if I wasn't overclocking.
As others have said, you definitely want a better PSU.
Instead of getting SLI, you're better off buying the best single card you can afford and then just replace it in a year or two. SLI almost never makes sense. If you don't go SLI, you could also look at non-nForce mobos (such as Gigabyte DS3).
I believe track was saying go with the E6420 and overclock it because the E6420 is much cheaper. Personally, I went with the E6600 as it looks like the best bang for the buck right now.
One note on the C2Qs. They aren't true quad core. They are really dual dual core. The Q6600 is very nearly two E6600 in one cpu. The problem with this is that each pair has to use the FSB to talk to the other pair (instead of communicating on-die which is much faster). True quad core C2Qs are supposed to be out in Q3.