It's possible it's heat causing the issue, but i'd guess it's quite unlikely.
However, the odd thing to me is that you say idle with the 7700 was <25C at stock, & under load when OCed, it's 55C.
That's a massive jump.
Likely mostly due to 7700 not being that great, but still, it leads me to wonder if your sensor is a bit off.
Anyway, i'd guess you've just reached the max of your CPU.
Keep in mind, not all of us with our 165s at 2.7 GHz are P95 stable.
SuperPI stable, sure, but i don't think mine would pass P95.