This is my experience as well. Running a 9920X @ 4.7GHZ on all cores. If I turn off HT, my average CPU usage in Cubase goes up 15-20% and peak usage goes up 25-30%. I am keeping HT enabled now. Motherboard is Asus WS X299 SAGE with latest 0905 BIOS, Windows 10 Pro for Workstations 1809 with latest updates.