Playing around with offset voltages, since manual OC means the CPU will be running 1.28-1.35V all the time.
Since manual OC showed that asking for 1.35V was stable, theoretically I could go back to MCE on, VCore Normal, and VID offset -0.100 (1.45V VID - 1.35V BIOS VCore for manual OC). Problem would be when the core downclocks to 800MHz and is asking for 0.700 volts. Not sure 0.600V will be stable.
Challenge then is to find a VID offset that brings VCore low enough under load that the CPU doesn't throttle too much, but high enough under no-load so it stays stable even when in a low-power state.
-0.050V seems to be stable under Prime95 and IBT, but it is seeing throttling under sustained Prime95 (eventually the 240mm rad isn't enough for the sustained heat output). Peak voltage during overshoot is 1.411V, some 0.025V higher than with the manual OC.

Going to try -0.060V, and -0.070V later...
Measured VIDs for reference:
