Didn't actually read it, just pointed out some highlighting stuff...
use HD103J, not 50xJ, Samsung Spinpoints F3's are a good series in total, just the 503's fail rate is real high, same thing with SSD, go with M4...
2600k is a much-go for a overclocking-designed CPU with a Z68, it will better use the HD3000 graphics with the z68 chipset but you got an external video card so it'd be stupid to go with 2600k, rather 2500k
* for that system, 550W is enough, 750 is overdoing, are you preparing for a CFx\SLI? if that's the case, why prepare for a dual core GPU first?
at that case, I'd recommand using ATI's CFx, it proves to have better results then an SLI on cheaper cards for mainstream games, and not performance, even though drivers tend to destroy that, it is usually a hotfix a week or two after game release, which is great
since series 7xxx is out, we can expect 6xxx price drops through the year, 6xxx is generally weaker then 5xxx equals, but it is cheaper and uses less power and less heat... therefore I'd go with 6850, it is strong enough on its own for advanced gaming, when you feel ready for CFx, buy another 6850 and you will be graphic-ready for 3-4 years of gaming at most advanced settings (which is alot! especially counting the 7xxx performance coming)
actually the whole build is based on a mistake which burns a lot of cash on wasted potential....try redoing it by using every bit of cash on things that uses their max potential (chipset to use the max potential of the CPU and GPU, but not going anymore) and then waste cash on better cooling, better\safer PSU, SSD\HDD or even CPU and GPU [though Mobo should be first]
also when choosing a mobo for sandy bridge, choose a mobo with more MOFOs, since the transistors get the electrcity before the processor socket, dividing it on more MOFOs drop heat and voltage unstabling and vdrops better than cooling fans and water cooling, which supports overclocking - the highlighting altername of the "k" series" is overclocking