How many screens are you gaming across? 4gb on a gpu would be overkill unless you´re up for high AA on three screens. Or do you happen to play BF3? The only game I´ve heard of, that would benefit from more than 2gb in a gpu (playing on a single screen).
If you save some bucks going with a 2gb gpu, you could put a little extra into the Samsung 830 SSD, a little more expensive than the 840, but overall performs a little better than the 840. Has a slightly slower read, but somewhat faster write. Is the extra performance worth the extra bucks...you decide.
The i-version of the psu has some fan speed/noise issues on Corsair link, you could search MeanBruceROG´s Maximus Owner´s Club thread for the issue.
And that´s very interesting stuff on the 670, Chino. I´ll definitely reconcider my choice of gpu. Thx