No, I don't think yer missing anything...that should rock. I mean, if it's primarily gaming, you might go 2500K, if you want to save close to a hundred. I use mine mainly gaming + surfing, haven't seen any bottlenecks or slowness. And the WD Black 1TB has 64mb cache instead of the 32 of the Seagate, but it'll run you (?) $15 more and I have no clue if you'd ever feel the difference. So just down to nickel and dime stuff, what you have will be great. I see you went whole hog on the PSU, again you could save ~$50 there and still be fine but what you have is quality goods no argument.
And 8G mem vs 16G mem, all you're likely to gain at 16 is compatability headaches. Especially so if you overclock.
Good on ya for stepping up to a 580. I had the same hard debate with myself.