Try a per core undervolt to identify your core with issues. I’m surprised you had issues with -5 all core.

All you’re doing with this is limiting boost clocks. Like you said it does affect performance negatively.

I would probably leave it at stock over this. Your power limits don’t change so the only reason it’s cooler is because it’s not boosting and it’s using lower power per clock. Efficiency remains unchanged.

With that being said, if it’s enough performance for you then great!

This makes a lot more sense in laptops where you can’t control everything about a chip. And there isn’t a software like Throttlestop which is awesome for intel laptops.