I am still feeling tired, and the effects of the beta-blocker mean that I am still out of breath at minimal effort, but I think I have suddenly hit a noticeable improvement. I just feel generally more like normal. I am regularly riding 25 miles on the flat and not struggling, I am finding it easy to keep to 130 BPM, even up small inclines or into headwinds. At work last week I managed two flights of stairs without panting.
It may be psychological but it is a genuine feeling of a higher level of fitness.