It will be worth it when we have 2x2gb DDR3 1800-2000mhz kits with decent timings for 100ish bucks.
And there are plenty of good 2x2gb kits out there... OCZ ReaperX, OCZ Reaper, G.Skill PQ, Crucial Ballistix. Usually one of those can be had for a great deal after MIR at newegg. I'd look for ReaperX first.
Looks good, however like we said before there's no point in getting the Q6700. It will not clock any better than the Q6600 therefore it's just wasted money.
And are you certain you are going to go SLI? Because the 750i is a great board, but there are better ones out there (intel chipset). The next gen cards are very expensive and extremely power hungry.
I would recommend a P45 chipset motherboard along with a single powerful GPU like the GTX 280 if you can afford it...or even the 9800GX2 which is better bang/buck than the GTX 280 at the moment.
Or with the P45 you could go 4850 crossfire which is looking like it may be faster than the GTX 280 and a heck of a lot cheaper.