See that's just it - there HAS been a marked improvement in applications performance as you've said, my 5960x will crush stuff compared to 4770k or 3820 x79 CPU, which is great, if you do that sort of thing. I don't, so it matters little to me (for now). I think you're correct, even Skylake won't make much of a difference.
I suppose it's just a matter of accepting that, and upgrading anyway at this point, it just seems...odd..I don't know, strange, that as you say SO much of the performance is based on video card performance, and any old cpu from the 2500k up to 5960x will do, and show little change in performance when tested using the same GPU.
If anyone would know why that is, I'm sure you do Skuzzy, since you're building a new game and all. It's systemic across the entire game universe now IMO, CPU matters little, GPU matters much. 10 years ago, even not that long, it certainly wasn't the case, it was a more balanced deal, in terms of new hardware, you sort of had to upgrade both CPU/MB and the GPU.