Can't get anymore T3? There are plenty of good sources --- Hell, it's legal to order! I wouldn't get too excited with the low dose theory. I've played with the following combo's based off low-dose theory:
T4 - 100mcg - actually went into hyperthyroidism for a week. Did little after I adjusted - no real difference on/off
T3 - 25mcg - as useless as 100mcg of T4.
T3 - 25mcg - combined with T4 - 100mcg - A little more of a boost.
I did notice, however, that when overtraining and cutting carbs even the T4 helped energy levels (no more naps at noon) and the overall feeling of well being.
If you're serous about cutting - at least in my experience - 50-75mcg of T3 seems best with a mild anabolic such as winny or even high dose 4AD as an alternative (500mg per day).