The problem is that stable curve optimizer settings can vary hugely across cores

I had differences of like 20 or more between different cores... i.e. one core might work fine at -20, the other maybe only at +5.

Most definitely - you should always do your own stress testing with your specific CPU (and system) to find out what's stable.

And while all core CO might not be optimal, based on personal experience and what I've seen across multiple enthusiast communities, more often than not you can get an worthwhile improvement to temps/perf with an all core CO.

That being said, there are certainly ways to find and set the best CO values per core, but it will certainly take more effort, stress testing and time.