Larry,
There are several reasons for the higher temperature thermostat. Mostly the higher temperature thermostats are used for a more complete combustion for emission controls. The more complete combustion may also increase fuel mileage, but not enough to notice. He probably installed the 195 degree thermostat because the 185 degree ones were out of stock at the time.
I think that the derate temperature is about 230 degrees. So you are not in danger of hitting that, and the engine should operate properly at 195 degrees, but I would prefer the lower temperature afforded by the 185 degree thermostat. I do not know how your shop feels, but I would not have changed your thermostat to a 195 degree unit without consulting you first.
Gerald