sometimes it can be a bit complicated. the 2500K itself should not be a bottleneck to GTX1060 GB even at stock clock. the issue is more on the CPU interaction with current gen of games. i still remember what happen with my system and AC Blackflag. at launch the game work just fine with my 2500K at stock clock with my 660SLI. when i got my 970 i tried playing the game from the beginning once more and i got stutter and frame rate drops from time to time regardless of the game setting (it was old game GTX660SLI and GTX970 is roughly about the same in performance). then i notice that CPU usage is extremely low. when they go even lower my frame rate start being affected (probably there were game updates that affecting CPU usage). after i was...
im sceptical because some people say it will bottleneck in games like bf1, and some dont, i dont want my gpu to go like <80 % usage
I posted a video of my system at the time (i5-4690K stock settings, GTX 1060 6GB, 8GB RAM) bottlenecking in BF1. It wasn't bad and it wasn't all the time, but I just wanted to share it because people kept saying there would be no bottleneck. See video description for full system specs.
Anyway, I would expect similar results form your 2500K @ 4.5GHz. *Actually, now I have i7-7700K + GTX 1070 + 16GB DDR4 and I still get similar performance (sometimes). I think they may have changed the game or something that has lowered performance. :/
sometimes it can be a bit complicated. the 2500K itself should not be a bottleneck to GTX1060 GB even at stock clock. the issue is more on the CPU interaction with current gen of games. i still remember what happen with my system and AC Blackflag. at launch the game work just fine with my 2500K at stock clock with my 660SLI. when i got my 970 i tried playing the game from the beginning once more and i got stutter and frame rate drops from time to time regardless of the game setting (it was old game GTX660SLI and GTX970 is roughly about the same in performance). then i notice that CPU usage is extremely low. when they go even lower my frame rate start being affected (probably there were game updates that affecting CPU usage). after i was sure about dropping CPU usage causing in drop for GPU usage and FPS i was thinking about increasing CPU speed to compensate the low usage. OCed my CPU somewhere above 4Ghz mark (later i settle for 4.5Ghz) and no more stutter.
current gen games can use CPU in much more complicated manner than before. when we see some dips in performance especially on older CPU we are quick to take that as bottleneck issue. but of course brute forcing by using much faster hardware most often solve the issue.