New 5800X3D user here... upgraded from 5600X on my X570 Unify board with the AGESA 1.2.0.6c BIOS. CPU cooled by an EK-240 AIO in a well-ventilated case.
Out of the box performance was excellent as expected, but I was concerned about high temps. At 1440P (3840x1600) in MS Flight Simulator flight, CPU temps were steady at 83C. Same with Cinebench 23 multi-core runs. In the BIOS, I have enabled CPPC and CPPC preferred cores, selected "low current idle" and reduced PPT from 140 to 125 watts, but there is no option to apply a negative offset to CPU voltage or (better still) to apply negative Curve Optimizer offsets.
The good news is, I found a freeware utility called "PBO2 Tuner," which allowed me to test various negative C.O. settings up to -30 per core. After stress testing I now have all cores except one at -30, with the outlier at -25. Bottom line: Performance is unaffected (actually a little bit better on Cinebench, from 14,6XX to 14,8XX) AND temperatures are better: down from 83 to 78C for the high under load. Per HWINFO 64, my VCORE under load dropped from about 1.25 to 1.17 volts. Fans turning slower, system is quieter, and I am now more confident in this chip's long-term durability. The only down-side is that the PBO2 Tuner settings are not persistent: I need to re-set the offsets with every logon.
So... if anyone from MSI ever reviews these forums, PLEASE give users the option to apply negative (ONLY negative) C.O. settings in the BIOS. This is NOT "overclocking" by any stretch of the imagination, so AMD should have no issues with it. Does anyone know whether the just-released 1.2.0.7 BETA BIOS offers any undervolting ability?