@Bex
I see you like playing ruff, with that poor dead MB of course
I didn't play much with x21, but I've seen a kind of jump/bump at 216x21 for 24/7 stability.
I've tried up to 220x21, and it boots fine (with PCIe= 100 ). It runs light load, and benches too with a "normal" vCore increase, but anything above 216x21 requires a big jump in vCore to stabilize for 24/7 use.
I settled for @4.51GHZ(215x21) 1.34v 10-run LinX on air because I couldn't stabilize the next BCLK with 1.36v.
This is for my CPU and RAM, and the limitation of my air cooling on this MB. It may be different for your setup. You should give a shot, it would be fun to see that @4.6GHZ beauty in 24/7 action.