This to report a positive outcome as above - and my thanks to those reporting good results on T3 only. (Paul and Co). Prior to reading about the possibility here I'd not realised that it was an option.
The past 18 months to late 2012 were problematical with several periods of months at a time of quite severe hypo symptoms - tiredness and lethargy, progressing on into stuff like spotty skin, cold hands and feet, low pulse, aches and pains, worsening gout and so on.
This after rock solid stability (if not great energy levels) since a thyroidectomy in 2005.
This I've strongly suspected has been down to recent variability in the potency and/or absorbtion of the major brand of synthetic T4 we get on the state scheme here. It's been reported as an issue elsewhere, but our system denies all.
Switching to generic brands last November greatly improved the situation - I was back to the prior 'normal' within a couple of weeks, and it's been dead stable ever since.
Knowing that my energy levels and my mood are still not what they were pre thyroid troubles (and facing some major work challenges) I decided to trial a higher proportion of T3 - raising the daily dose from 150mcg of T4 and 20mcg of T3 to 50mcg of T4 and 45mcg of T3. These are roughly equivalent doses based on the x4 rule of thumb for estimating the equivalence of T4 and T3 doses - but the latter contains a higher proportion of T3.
I have to say that I've been pleasantly surprised at the result. Two weeks in my energy is much better, I'm waking properly in the morning and my mood is improved. I feel far more lively and pro-active than before. My gout has faded. Even my sight is better - more stable, and somehow brighter.
Next up is to bring my (usually constructive) endo on side and get it prescribed longer term.
Care is needed when making the transition. The half life of T4 is perhaps 7 - 10 days, so if the dose of T3 (which has a half life of perhaps a couple of days) is upped to the nominal replacement value before the T4 has cleared the body there is a real risk of ending up significantly hyperthyroid/over replaced in the first days. i.e. it's advisable to ramp the T3 over about a week. It's presumably vice versa going the other direction.
I'd always known that increasing the amount of T4 I took left me feeling awful, but I'd always somehow presumed that the relatively low proportion of T3 was fine for me - and that my longstanding less than great energy was down to side effects of the auto immune issues/food sensitivities I'd developed over the the many years of undiagnosed hypothyroidism prior to my thyroidectomy in 2005.
It's early days, but it ain't necessarily so it seems.
If I have reservations it's the relatively short half life and more restricted availability of T3. It seems i need to stage the dose of T3 in lots over the second half of the day (a bit of a PIA), and even at that there's some sense of 'falling off the cliff' in the evening. Plus I'm not so sure about reliability of supply in the event of say economic or other turmoil or instability in the system.
I'm wondering at this stage if I dare go the whole hog to T3 only, and if it might deliver further improvement - or if maintaining a fairly minimal 50 mcg of T4 is buying me anything in terms of greater tolerance of any gap in supply that might arise.
Comments appreciated, but my thanks again to the community.
ian