Yeah, from what I've heard about the i5 6600K you can get it between 4.6-4.8GHz. 4.8 is pushing it, though.
I'm planning on using AI Suite 3's 5-way optimization. It's got some good options in it, like a per-core overclock, etc. and it also tests your cooling, runs stability tests and then after it crashes and your pc restarts, it once you ok it will enter the last safe settings in the uefi for you.
Now, if I do decide down the road to get a EKWB Predator 240, then I'll try the 4.7, but I'll be happy with the 4.6 overclock.
Heres a video on the 5-way optimization.