If you have a pure gaming pc, then a I7-7700K with an overclock will perform exactly the same.
I might suggest for pure gaming that the i5-8600K which IS available will perform the same in gaming. Few games need more than 2-3 threads so the 6 thread 8600K will be fine there.
If you also run multithreaded apps like editing, then the extra threads of the 8700K will be better,
and waiting for availability is probably best.
I7-7700k needs a z270 motherboard, and a I7-8700K needs a Z370 motherboard.