GPU is a close to GTX 1060, still very capable at 1080p level. 2600k is still fine for 1080p 60hz gaming, but if you want to upgrade, CPU first.
If only gaming, I5-8500, B/H/Z 3xx MB and 8gb ddr4 ram depending on your budget.
Do you overclock? If so, I5-8600k is better with Z370 MB. GTX 1080 is better with 1440p 144hz monitor.