Note that upgrading to a 7th-gen i5-7600K (coming from a 4th-gen i5-4590) means replacing your motherboard and RAM kit as well, which will cost a LOT.
Have you considered just sticking with your 4th-gen platform, updating the mobo's BIOS, and changing just the CPU to a Haswell-Refresh 4th-gen i7-4790 (or i7-4790K if you do have a Z-chipset mobo)? This will cost you less and would alleviate issues on CPU-intensive games.
If you really want to overhaul your rig, consider also migrating to the Ryzen platform, such as the Ryzen 5 1600 (6-core/12-thread CPU and unlocked/OC'able) instead of the i5-7600K, at $30 less (for the CPU). You'll also gain some savings in choosing a B350-chipset Ryzen motherboard, which is already overclockable, compared to the more expensive Z270-chipset Intel mobo for the i5-7600K.