Ok I have already done some quick testing. This is with a youtube video playing in firefox (I moved firefox back to p-cores for this testing).
I set min unparked cores to 50% in the power schema, which basically parks all the HT cores (2nd logical core for each p-core) unless a all core load in which case they unpark, I would have to set max unparked to 50% to force them parked under all loads. I then watched the load how it was allocated, I am posting two screenshots, the first is with HT cores parked, the second is with all unparked.
Logical core number starts at 0. 0,2,4,6,8,10,12,14 are the first of each p-core, 16 through to 23 are the e-cores.
8 and 10 are the preferred p-cores (highest clockers).
Result is interesting, different to what I thought was happening, it seems the load pushed on to the HT cores, is only happening on the preferred p-cores and the load pushed onto cores 0,2,4 is the same with HT on or off. (a all core cpuz bench correctly unparked all cores)
What I plan to do.
Cinebench run with HT cores force parked, to see % impact on score as well as max power draw difference.
Test various games to see if stuttering issues are worse with HT on or off. The gaming I have already done on this CPU with HT on in its default state is much better than it was on my 9900k, but I am curious if it is as performant with HT disabled.
This is different to disabling in the bios which makes the HT cores totally not available, I prefer OS side control, as it allows switching behaviour live on the system.
This test was done with the windows scheduler set to "prefer performant cores".