Not every i7 can be overclocked. Only the K versions. For gaming, a i5 is fine. But if you're going to do any bit of streaming or video editing I'd totally go for an FX 8320 8 core. Super good value.
Lol'd pretty hard at Goat_'s comment. "Just to make your e-penis bigger" pretty much haha. But for tf2, I've heard that overclocking the cpu can increase fps by a ton.
Why no amd cards? Oh don't tell me, he's an nvidia fanboy... Of course a mac fanboy just goes from mac to intel/nvidia. Pretty much the same stupid fanboyism. Amd gpus are faster. Period. For a $2000 build he could probably afford either, but amd is going to be much better. Is he okay with crossfire/SLI? A SLI 670/680 or a crossfire 7950/7970 would destroy, if he can afford it.
Windows 8 is actually pretty awesome, much faster all around and once you get some programs to get back the start bar, it's just all around better. Metro interface does suck though, I removed it (the tablet windows phone interface screen, with the tiles).
Spending $2000 is overkill, he could probably do fine with just a $800 build, maybe a 7870 and a 8320/990fx mobo. Unless he wants to push 120fps on crysis 3 on ultra 1080p, or go multi monitors it will be fine. My 660 can run metro 2033 at 40fps and crysis 2 at 60fps, fine by me. But an overclocked 7970 or 7950 (or 680) would probably do better.