One of the outstanding deficiencies in thyroidology is well conducted studies of Quality of Life (QoL) against FT3 levels in T4 treated patients. A recent study (Pol. Arch Med. Wewn 2016; 128 (4) 293-296, doi: 10 20452/parriw.3392) has shown very clearly that there is a strong relation between T4 dosage (thus FT3 production) and QoL. It further shows that in a few subjects FT3 does not rise when T4 dose is increased and thus such people would benefit from T3 supplementation.. This is a very well conducted prospective study. It shows clearly that TSH levels should not be much of a concern in setting a dose level for better QoL and that many subjects had below range TSH to get there. Though this is only a small paper, it is of major significance in the battle to understand and treat thyroid deficiency more effectively.
If you cannot access the paper direct, then I've sent Louise Warvill a copy.