In the comparison I saw, Broadwell-C outperforms by an inconsequential amount in games that are CPU bound (5%). So yes, with Broadwell-C you can pace Civ 5 etc at 125fps instead of 119fps. Those are meaningless numbers from a playability perspective.
I wouldn't call them meaningless. Regardless no-one said there was a huge difference or that you should bother.
Even the i7 4790K isn't far away from the i7 6700K Skylake one so you could even go with that which is also cheaper.
And speaking about prices and old models the i7 5820K would likely give 6700K a run in modern game titles too.
If you go further back the i7 4770K, i7 3770K and possibly the i7 2700K isn't terrible and far away either, per generation at least. You likely got like less than 10% of extra performance for each new one. And that's when you ignore 5775C (as in 6700K not being 1.1*1.1 times better than the 4790K.)
That a supposedly uninteresting chip with better integrated graphics clocked at 3.3 GHz can outrun the newer chip on the new platform clocked at 4.0 GHz in gaming was a surprise for people.
Speaking of over-clocking and the 5775C vs 6700K the 5820K likely over-clocks very well as-well (The metal capsule/lid over it is supposed to be soldered on that one if I remember correctly, the 8-core one over-clocks nicely and the 6-core one should have an easier time I suppose unless lower quality.)