Moving this argument forward, surley there must be some way of calculating an input v reward curve to work out the optimum input (i.e. effort) before the increased fatigue outways that increased effort. That could be trialed now as he is riding a fairly consistent daily mileage. This would then give a more accurate idea of how much effort can safely be put in later when he starts to increase not only affort but time in the saddle, but also the mileage.
I'd argue that Steve has basically done this already through his previous high mileage years and arrived at the effort level that he's been riding at to be his optimum. So your point is a valid one, but Steve is way ahead of you in working it out :-P
