That build looks great and it will make the world of difference, that build will max any game on ultra high settings at a playable FPS, i know it because every part is a bit better than mine and i can max anything.
Probably worth it to get an after market cooler for the 2500k for overclocking. CoolerMaster Hyper 212+ ~$30 from amazon with free shipping ( cheaper than newegg ) for example will do great.
The MOBO is no good though, it doesn't support XFire or SLI. the GD53 does but unfortunately the G43 does not, GD53 is quite high priced though. So here is a nice alternative. Gigabyte GA-Z68A-D3H-B3 at $129.99 does support SLI/CrossfireX and it and also comes with the Z68 goodies.
The PSU is good and should be able to run a 2nd 6870 just fine.
the corsair is 1.65 V which i heard is bad for the memory controller on sandy bridge i probably wont go that far on overclocking tht i would need a aftermarket cooler and on the msi website it says it supports crossfire and on the SBM for the 1000 pc they used this mobo whith two 6850s and the mobo u reccomended is 125 while this one is 80 after the 40 combo discount
I do apologize for that, the ordering on the MSI web page was odd to say the least and checked the wrong board( C instead of G ).
It does indeed support sli & crossfire, I stand corrected.
As for the memory yeah, should be a 1.5V kit as suggested. Check for sales tough, plenty of 1.5V 2x4GB CAS9 1600MHzkits have been on sale in newegg lately. At roughly the price of the kit that was listed in the post.
Due to the combo deal with the HDD and PSU it's probably hard to beat that.
However there is currently a promocode PSU624 that gives you 10% off of corsair PSU's and atleast in my basket it gives $11 off which would pay for that difference. Not sure if you were using that yet, or if it works for you but give it a shot.