My 5900x more or less a toy in the end. I'm on 1440p so I don't think the end clocks for me will make much difference in gaming, but I still have to check the fps when I'm underclocking my cpu.but i have since settled on 4.4ghz since it required almost 0.1V less.
I believe my uEFI settings are as follows. PBO on advanced, all sub-menus are auto, curve optimizer disabled, load line setting 4 the memory is running at 3800/1900. I found no reason to disable SMT on my rig.
Using CBr20 as a quick test.
Using the latest free version of CTR 2.1 it came up with this profile. It's the 1st time that it's actually given me a tried and true stable profile.
I guess it does prove your point in the end as far as clocks vs voltages go. I'm more or less concerned with temps in the end as Summer is just around the corner. 20c drop was impressive without loosing any performance in the above scenario.