Help on first time build

Hello,
I'm building my first computer and I usually just get the shop to do it for me but I've decided to give it a try myself. It's for gaming and my monitor is 1080p. I've read online, reviews etc and I've decided on these parts:

Motherboard: ASUS P8Z68-V B3
Video: ASUS Radeon HD6950 DirectCU II 2GB
CPU: Intel Core i5 2500K
RAM: G.Skill Ripjaws X F3-12800CL8D-8GBXM (2x4GB) DDR3
PSU: Seasonic X-650 80Plus Gold 650W
Hard Drive: Samsung SpinPoint F3 1TB HD103SJ
Optical Drive: ASUS DRW-24B3ST 24X DVDRW Drive
Case: Corsair Obsidian 650D Case

The case is expensive but I like the look of it and the "user friendly" design, this will be my first time and I'm only going off youtube videos. My question is, are these parts any good? Are they compatible with each other? Is the PSU powerful enough or overpowered or just right? or is there something else out there that is better in performance and cheaper? My budget isn't too limited and I'm not interested in crossfire because I heard most games barely utilise the technology and I wouldn't know how to set it up. On a final note, I wont be overclocking either, I just simply dont know how and if any of these parts are for a overclocking build I would be grateful if you could point it out.
Thanks in advance.