I5-6600K with an overclock is about as good as it gets for a gaming cpu.
Few games can use more than 203 threads, so I7 is of little value as an upgrade.
If you are gaming at 1080P, GTX1070 is very good.
Only if you favor fast action games or want to plat at 1440P might a GTX1080 be useful.
Actually, if that were the case, I would wait to see what GTX1080ti will bring.
If you do not have a ssd, consider that as a very satisfying upgrade.
It makes everything you do feel quicker.