I have never built a computer before, but after much research and great help from the community, here is my first build. Computer will be used for games like SCII, Diablo III, BF3, and the new Mechwarrior online coming out. Any advice would be great.
Get a cheaper mobo, such as the ASRock Z77 Extreme4, and put the extra cash toward a 7870. You can also go with a good 650W PSU for 7870 SLI, or a 750W if you've got the urge. 850W's overkill, though. You also might consider a cheaper case. That should be entirely a matter of stylistic preference; don't worry much about one case being "better" than another.
I'm not totally certain about the EVO and the RAM, but I've never heard of anybody having an issue with G.Skill sticks.
Looks good, I'd get the MX-4 thermal paste over the Arctic Silver 5, it performs slightly better and its the same price. I'm not 100% sure on the RAM clearance but the heatsinks on the RAM is almost ineffective and if you can find some low profile RAM of the same specs for the same price I'd probably go with that.
Get a P67 mobo (like Asus Maximus IV) instead and go for 7870 like kajabla said. You don't need also 850w PSU for this build. 650-700 is enough. I would take sandy bridge instead of ivy like 2500k after OC is better than 3570 OC. 2500k is about 30$ chaper and the difference between these two CPUs is around 4% There is also overheating issue when OC with Ivy Bridge.
IB runs really hot. Good luck getting to 4.5 without water. Then again I don't like my components running hot for daily use because I want them to last. I know AMD and Intel temps don't compare but I run my 980BE at 52C max load and 55C is my absolute max. I've helped three people get to 4.2ghz on IB with ease, the only limitations was what I thought was excessive heat...
Lets get back to the OP. They're both good chips. The stuff you picked out will be a great system. If you're not on a tight budget then go with what you have. If money is tight you can downgrade certain items and upgrade others for better gaming performance.