Is the cpu Q9400? It's alright, but I'd go with Q6600, especially if I'm overclocking it.
Are you gonna SLI? If not, pick out a P45 mobo by ASUS. Seems you like that brand.
750W is enough for dual GTX260's, but not 280's or 285's. I'm saying if you upgrade the 260's to two more powerful cards, the 750W may not be enough. 1000W+ will be.http://www.slizone.com/object/slizone_build_psu.html