Very good build, overall. Couple of observations. I take it you are using a 750w power supply, to give option to add 2nd graphics card, in SLi. If not, you don't need anything like 750, 550w would be more than adequate. If you change, stick with good quality, though.
The Extreme 6 doesn't give you a lot, of real value, over the EXtreme 4. At the price of the 6, I might be thinking of an Asus P8z77 option, although, of course, I don't really know how prices vary, for you.
Ivybridge + Z77 are able to use 1600MHz Ram. Whilst it doesn't give a HUGE gain, it's worth using 1600, if the price difference is small.
I'd give it a 8 out of 10 for that price range. You got some good quality parts there. Only a few things I would change the hdd and ram. Should of got a western digital hdd and 1600mhz ram. Also a ssd would of been nice. You could of got a smaller hdd, little bit cheaper case and psu then added a 128gb ssd for the os and games.