I'm good with making any changes you might recomend. I'm not too confident in my picks at the moment and am looking for some guidance (particularly around compatability, being able to fit everything into the case I already own, and having enough power for the rig).
Also, don't really know the difference between the two GPUs I mentioned besides the price point. Never had a SSD before, but they look to be pretty cheap so I figured I would pick one up (how much space do I actually need on it?).
The 7950 is a step down the top of the line 7970. Since its only a 30 dollar premium, plus the fact that its a good overclocker which allows you to get its performance close to the 7970 (watch out you can void your warranty by doing it though), I think you should get it over the 7870.
Max power draw of a 7950 is 179W. All else considered, you'll be fine with a 550 - 650W PSU.
For a MoBO, the Asrock Extreme 4 is for SLI/Xfire setups. The Asrock z77 LGA 1155 Pro3 or Gigabyte z77-d3h LGA 1155 Motherboards would be good for a single card setup.
Ive seen some posts indicating that the 2500k is a better bang for your buck due to its easy OC.
That's a very nice build you have up top in the OP. I wouldn't change a thing although it could be a tight fit with that Antec 300. I would go with the Kingston 120GB SSD and if you are looking to cut any cost off that build without taking a bite out of performance then check out the links below these 7870's. That would gain you another $50 to put towards a case and/or SSD and you would still be getting 7950 performance with a slight over clock. And no I wouldn't drop down to the 2500K. You lose out on native 3.0 USB, PCI-E 3.0, not to mention some other goodies that come with the Ivy Bridge and the Z77.