If you previously had 37x and 120MHz, the math looks like this:
4440 MHz = 37 * 120 MHz
This is closer to a 44x ratio than to 45x when using 100MHz. This might be where the difference in needed voltage comes from. You sadly can't configure something like a "44.5" ratio, but what you could try is using 101MHz instead of 100MHz. The math would be:
4444 MHz = 44 * 101 MHz
Perhaps try that and see if the clock is still slightly freaking out when using 101 MHz.
Personally, I think I would just stay at 100 MHz and use 44x.