Richard, There is nothing to be gained from dropping the pressure it only makes your compressor less efficient. Depending on pump design and driven speed the design shut off setting is optimized for that tank size and HP rating and to change this setting only wastes power. Sorry but I have sold and serviced compressors and air systems for both shop and mobile maintenance rigs for about thirty years and it has been my experience that tinkering with that pressure switch usually leads to trouble and rarely if ever provides any benefit. As far as the regulator I would never tell anyone to exceed the max inlet pressure but I have seen many such regulators run for years on settings higher than 175 PSI with no problems, some as high as 250 PSI
I have no personal experience with that Jet but 15 PSI over pressure is not very likely to hurt anything and that Sharpe would in all likelihood stand a great deal more than that, I can safely say there are thousands of them at this minute hooked up to 175 PSI and higher.
As an added note since I have mentioned these higher pressures, I am not saying it is ok to run higher than 175 PSI and in fact I have for years warned against this but it is a fact that a lot of people do. It is a bad idea because it is not only dangerous but there simply is no logical reason to do it. That shut off pressure was chosen by the engineers who designed that compressor and not by the shop janitor so if there was any major benefit to any other setting then that is the way it would have been supplied. My advice based on over thirty years experience with these things is to leave that pressure switch alone.