9965 cTDP = underclocking?

[fatherboard]

The Epyc 9965 (192 cores) seems to have a configurable TDP (cTDP) of 450-500W, right beneath TDP 500 in the specs page. Is it something I can manually choose to do to bring down the TDP to the cTDP 450?
I've found an AIO cooler that could possibly handle the 9965, and claims to handle up to TDP500 but if and only if, as per the manufacturer, I do not overclock or do heavy things with it. Well I will definitely do heavy (perhaps the heaviest) things with it. If I have the possibility to set the cTDP to 450-500, am I underclocking it? if that's the case, is there a way to find out how much performance I'm loosing with cTDP 450-500?

Note: The dual 9965 will get plenty of room to breath in the Silverstone Alta D1, and I will pay attention to the environment temperature (motherboard manufacturer said max 25C).

 

[RolloZ170]

BIOS setting cTDP

 

[fatherboard]

what about performance? how much am i loosing for the lower cTDP in general? I'm asking because if it's going to slow down to the equivalent of e.g. 128 cores performance, I'd rather get a 128 cores and use the big price difference for other components.

 

[RolloZ170]

what about performance? how much am i loosing for the lower cTDP in general?

perf. scales with TDP in that area, lower TDP = lower all core clock.
but lower clocks are more efficient.