I overclocked a 4100 to 4.4Ghz on a UD3. I had to update the BIOS and disable APM. I also had to set the load line control to "high" and use a +.025v vcore offset. (I, used a push-pull TX3 for cooling on that rig.)
I didn't even attempt to OC with the F5 BIOS because I saw the thing throttling down to 3.3 in prime95 stock.
4.6 might have been "doable" but it wasn't my rig and I wanted a safety cushion.
As for the change in default voltage, I think that changes with speed, automatically.