Just finished reading this thread, found out some really interesting info!
I'm currently debating a CPU upgrade. Right now I have a 4670K, but I think I lost the silicon lottery quite spectacularly as I can only get 4.2 out of it (and that's with over 1.3v) so instead run it at 4.0GHz @ 1.29v. This was the first CPU I bought, and back when I put this system together it was touted as the right chip for the job (as capable as the 4770K for gaming and a lot cheaper).
I've been bitten by the upgrade bug, and now the only part of my system that hasn't been touched is the CPU / mobo. My use of the system has changed too - I do quite a lot more 'work' on it now, as my degree involves a lot of Visual Studio and Unity. Unsure as to whether they benefit from additional cores or not, though.
Anyway, I upgraded my old GPUs (pair of 780 Classifieds) to a pair of 980 Ti Hybrids during the Black Friday sales. Regret getting two, to be honest, but that's another story. The thing is I now feel that my CPU is the weakest link in the system, and have noticed a lot of occasions where my FPS drops significantly. As my GPU is often nowhere near 100% usage I wonder if this could be an issue with the CPU.
So I've been looking into upgrades - everything from the 4790K (would be as easy as dropping the new one in!) to the 6700K and 5820K. After reading this I think that my preferred route would be the X99 platform, as having the 5960X as a potential future upgrade sounds amazing and I think of the 3 choices it is the most 'future proof'.
My only concern is that I may end up with another really bad overclocker, particularly as the base clock is relatively low. I have found a couple of places here in the UK that offer a service whereby they actually guarantee a clock of 4.4GHz. But of course, you pay extra and in this case I'd need to buy the same cooler I already own!