There’s also the issue that newer cores run much hotter than ever before. The chiplets in my new Ryzen 7 5800X are so small that even my custom water loop can only do so much with the temperatures as there just isn’t enough surface area for thermal transfer. I was honestly worried that I was repeatedly messed up the mount of the CPU block, thermal paste application, or that one or both were just bad when I fired up HWInfo64 and did a burn-in test; my old Ryzen 5 1600X didn’t get near as hot on a 240MM AIO when overclocked as the 5800X does doing normal boosting on a 360+240mm custom loop.
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.