What is the best process to tune an Apollo miner?

I have a more powerful PSU available and have reduced the noise to low enough to run 2 Apollos in the bedroom.

How do I find the maximum heat output and hashrate without drastically reducing the durability of the ASICs?

I can easily find the highest power setting that allows me to run the miner with an acceptable noise level, but how do I determine the best hashrate for that power level?