First, I wouldn't call it an extremely high end, nice build tho.
You will need an aftermarket CPU cooler if you plan on doing some reasonable overclocking, Hyper 212 if you're on a budget, or get a closed loop water solution if you can spend a little more.
The 780 will push good FPS in all games for the foreseeable future.
Agree you need a cooler. If you want to save some cash, there's nothing gained from going for more than 2x4GB of RAM. On a gaming machine, the vanilla Samsung 840 (or 840 Evo if the cost is the same) will be just as fast at loading games, virus scans, etc as the Pro (it's only advantage is write speed which you'll rarely do).
Your mobo is fine but it will probably OC a couple hundred MHz less, but there's no guarantee. It's not something you'll actually notice.
5GHz is no guarantee on a 2500K and mid-4's is no guarantee on the 3570K. Each chip OC's differently but you *should* see 4.3 at least on the 3570K. I went with the 3570K since it's supports PCI-E 3.0 (2500K doesn't) and tho it doesn't matter now, it might down the road before I swap systems again.