I've always heard that a cold running engine (ie: not operating within the temp range it's designed to) accelerates wear too (but not overnight). Don't know exactly what the scientific reasoning is behind the declaration. However, I can say that since an engine is a big heat pump it needs to run at upwards of 200* for efficiency. Also, you need higher temps to burn off condensation that forms inside the engine - amongst other things. I'd make 180* the minimum.
It's also a common belief that if a car overheats with a 195* stat, then switching to a 180* or 165* may cure the problem. Assuming the 195* unit was opening correctly, switching to a cooler thermostat won't fix anything. It'll just take the engine longer to overheat. Best to investigate why.