Mitigations can have very large effects on system stability, I ran into this with my old Haswell system. Mitigations on allowed, I believe, 100Mhz higher at lower voltage - but it may have been 200Mhz. These settings were tested over many months, completely stable, and mitigations off with the same setting wouldn't even allow booting. Huge effect relative to anything else, basically like adding an extra 0.1V vcore.