T4 is pretty useless.
The body has to cleave of a molecule of T4's structure
to convert it to the meatbolically active T3.
(T4 has very little metabolism boosting properties)
You reasoning is that: The more T4, the more T4 gets
converted to T3 right? Actually wrong.
The body converts T4-T3 at a measurable rate. When
exogeneous T4 is introduced, the body DRASTICALLY
reduces any extra T4-T3 conversion. So, the
T4 has pretty much no effect.
T3 is already metabolically active, so it is a far
better choice. Not to mention its far stronger than T4.
Te half-life of T4 is also FAR, FAR longer than T3's
(4 hours), making it a pain in the ass to administer.
Godspeed