I'll add my two cents here. I took a different approach. I forced Windows (and all the programs running in Windows) to only use four cores and eight threads. This can be done by typing "msconfig.exe" in the Search bar (next to the Start button) and opening up the configuration utility. On the Boot tab, look for Advanced, then set the maximum number of processors (actually threads) to 8. This video details the process:
According to task manager, this forces the Windows to only use half the available cores and threads on my i9, effectively turning it into an i5. This has a triple benefit; it causes the CPU to use less power, generate substantially less heat and hit higher frequencies, which is often more important to games than total number of cores. Using less power and generating less heat also gives the GPU more thermal and power headroom.
I haven't done formal benchmarks, but a casual test in the game Control saw my 4GB 5500M hitting 1150MHz - 1200MHz and frame rates in the mid- to high fifties. The game was running at 3072x1920, with a render resolution of 1920x1200, high textures and a mix of low and medium lighting & effects. I'd post a video as proof, but the January 2020 Red drivers at bootcampdrivers.com don't seem to support video capture.
Obviously this will limit the amount of CPU horsepower available within Boot Camp. So this approach may not be suitable for people who do serious work in Windows. But I use Boot Camp for gaming and general use, not anything serious like video editing or running a dozen VMs. I'm also using the Windows version of Macs Fan Control to ramp up the fans pretty early. Though some might not like the noise, I can just use headphones if it bothers me.
