Finally got a decent voltmeter and it's taking a lot of the guesswork out of this fun!
One of my Terminus only reaches 3.07V with the potentiometer at max. Now I know why this one won't hash reliably over 200MHz.
Needs a steady 3.02V for the next step up 225MHz.

Now, does that mean with a better power supply it could get more power to the chips and hash above?

Got the V to MHz from this:
https://bitcointalk.org/index.php?topic=1845307.msg27843112#msg27843112