No difference ? Really ? I went from a FX-8370 4.7ghz to a 6700k 4.7ghz and my games nearly doubled fps, programs like video coding are MUCH faster and I noticed a definite speed bump in overall Windows. Unless you're using the computer only for web browsing (or are GPU locked) you should have noticed around 25%-35% extra performance ?
http://cpu.userbenchmark.com/Compare/Intel-Core-i5-6600K-vs-Intel-Core-i5-2500K/3503vs619
When I was testing [email protected] and [email protected] APU then both were in some games as fast as stock i3 [email protected]. It's obvious that after moving from AMD to Intel you see performance difference but going from 6600K to 6700K or 6800K you will barely see it. At least I passed 6600K, 6700K and 5820K in my gaming PC and I see no difference. There is visible difference in some games between i3 and i5 but not between i5 and i7. Actually now I play on 3770K which was collecting dust for some time and I also see no difference in games between it and Skylake i5/i7. What matters is to have ~4.2GHz+ and Intel quad core CPU. Everything else depends mainly from graphics cards. Also SSD helps more than moving from 4 to 6 cores. I mean any SSD, it doesn't matter if you get average series or the fastest pcie model.