what is the most powerful intel cpu + motherboard that will support mojave?
That i9 CPU is 12th gen. Don't expect it to work with Mojave.with the 10th gen (e.g. 12900k)
You'll get more out of a 12900K when using Windows. In macOS you have to either disable the 8 e-cores or hyperthreading to get it to work at all.Or go the Windows path and forget the Mac OS.