Hey,
I'm new to new to overclocking CPUs, but I decided to overclock my i5 6600k and see how far it goes. Well, at 4,4GHz @ 1.35 (probably excessive), I got it running without any crashes whatsoever. However, while running IntelBurnTest, I noticed that after around 20-30 seconds, the clock speeds dropped to around 3.0-3.2GHz and stabilized there. The CPU temp was around 60 degrees Celsius. I've a Noctua NH-U14s cooling the CPU.
Any ideas what could be wrong?