In 2009 I overclocked my i7 920 from 2.66GHz stock to 4.2GHz fully stable with custom water-cooling. More recently I have used i7 7700k and Ryzen 5950X under custom water-cooling and manual overclocking gets you less than 10% at most. Hardly even worth it. Just keep the CPU cool and let the built in boost features work.
Now you're making me nostalgic. 10-15 years ago was both my teenage years and the end of the overclocking golden era. I remember overclocking the living shit out of all kinds of Core2 stuff without anything except a stock cooler and a modest voltage bump that was still within Intel's "safe" recommendations.
One of the best gains was with an E5200 I spend around $120 on brand new. Bumped that up from 2.5GHz to 3.8GHz and the performance was closer to a then-$300 E8400 than the low end Pentium I'd purchased.
The last CPU I overclocked was an i7 2600k, which was my daily driver until last year (!!!).
On one hand, I miss that crazy era, but on the other hand I understand why it had to go away. Intel just don't have the sheer performance advantage to be able to gimp their own chips like that any more.
Edit: Just remembered some of the gimping AMD did, like the HD 6950 that could be upgraded to a 6970 with nothing but a BIOS flash, and the "3-core" Phenoms with a 4th core that could be unlocked in the BIOS.
I also remember buying a cheaper GPU from ATi, because the rumor was that it was a binned high-end GPU with very little defects that was only soft-locked. Worked like a charm.
It's still not clear to me why they did that.
But in any case, suddenly the thermal performance of Intel CPUs dropped significantly, which gave rise to the de-lidding phenomenon.
Now that Intel has switched back to a better TIM the era necessarily is over.
10-15 years ago folks did more overclocking but there wasn't really a need to de-lid, it was more about heat dissipation via elaborate cooling setups than messing with the chip package itself.
This one I have now is the first one I haven't overclocked in at least a decade: i9 10900K.
I went from an i7 8700k running all cores at 5GHz to the i9 10900K running stock.
The reason was that I ran HWInfo and saw that it clocked to almost 5GHz on its own with single and dual-threaded workloads anyway. And given the 20 cores, it would hammer through anything that needed multicore.
In short, this is the first time I didn't feel the need to overclock.