That trying to prolong life of asics is bullshit...
That gear will be not usable after 6 to 12 months, so just get the max from it and don't care for their life.
I push them to the max and trying to mine as much is possible before next gen was released.
I have 2 sp20e and im lucky so far to not pay for electricity where they are located.
I sett one fan to 100% but second to 80% because there is very annoying fan resonance if both are set to 100% and that resonant noise can be heard behind wall.
My pair of s-3's have run non-stop since july I have them underclocked to freq 212 the two total 850gh and they pull about 650 watts. the power cost is 2.4 cents a kwatt.
So I am doing the exact opposite of your advice. Since the cost to run the pair is 15 usd a month and they earn 75 a month I am netting 60 a month in usd.
I would hope to run these for 18 months .
at a diff of 126 they would pull in 27 usd a month and cost 15 to run. I think diff of 126 will not happen until jan or feb of 2016. So I nurse mine.
But to each his own as your plan may work for you.