I have now had quite a good run after a lot of headaches at first with crashing and odd behaviour at stock settings. I was scared at first to try any higher settings but eventually got the courage to give it a go. The ambient air temps of the area it lives in fluctuates between 24C and 32C. When the ambient air temp is at 32C the miner does reach 64C, but these screenshots were taken at an ambient air temp of 26C. Also I am just using the stock PSU on 240 Volts.
You should know
...about Voltage: You can set there what You want, because it has no effect and does not change real voltage of PSU. If You watched cgminer script in S4 unit You knew, that there is always set the same value 0725.
...about S4 PSU: it is 80 GOLD PLUS PSU, running at the very top of its abilities. If You overburn it (by changing voltage via ssh in cgminer script), You can damage it, and I would like to see You how are You replacing it.
...about GHs hashing power: overclocking is lowering efficiency rappidly, if You get 10% more GHs, You loose more then 10% of energy at the same time. No more words about hw errors growing volume. I do not see any sense doing that, but if You want to play, play.