5000 Series Undervolting

[The Asgard]

It's because curve optimiser is naff. It's sold as an 'undervolt', but in reality it's just a plain overclock. When the CPU boosts it will request ~1.45v and set whatever the maximum frequency it can, up to the boost limit. For most CPUs, they can't sustain the boost limit (they spike to it briefly, but not sustain). So curve optimiser results in a net frequency increase, but no voltage reduction. IMHO, that's not an undervolt.

On a 5950X I observe CPU temps that are 8C higher with curve optimiser at -20/-30 vs when it's disabled (but PBO still enabled). CPU power is +25-30 watts higher with CO on. I just use fixed overclocks myself too now. Seeing some good results with 4575 MHz at 1.175 V and CPU temps are pretty nice indeed

There is a lookup table just like the VID that gives you a per core voltage for a given frequency. The voltage supplied at a specific frequency is offset by the value. This is an undervolt. You can boost higher because less heat is generated for a given frequency.

It’s definitely not Naff.

 

[The Asgard]

It's still way hotter and spikes to 1.4v

Have you tried using a negative offset, this is not CO?
That's better than a fixed voltage because you get the benefit of reduced voltage a low frequencies which should run cooler and use less power. Just adjust the negative offset to give you a 1.25V load voltage. You might have to throw a bit of LLC love in there but should be easy. You certainly have some options if you don't mind playing with a few settings. This is old school Intel stuff.