When do you think a lower thermostat is a good idea?
Pretty-much
never.
If the engine overheats with a 195 thermostat, and
it's not because the thermostat is faulty, it'll overheat with a lower-temp thermostat. The issue is that the engine can't shed heat as fast as it's being produced, and the 195 is already wide-open. Therefore, a 160 would be just as wide open, just at a lower temp. With less difference between engine coolant temp, and ambient temp--there's even less heat transfer. So the temp continues to creep up until it reaches equilibrium, or the driver gets scared and shuts off the engine, or the engine seizes.
Semi-trucks and buses have enormous radiators--the vehicle is intended to run with the throttle pinned to the floor for potentially hours on end. The radiator is sized to handle WFO operation. Passenger cars and light trucks have relatively small radiators for the horsepower the engine can make, the radiator is sized to handle part-throttle operation. WFO operation results in temperature climb--short bursts are fine because of the mass of the engine and cooling system. Extended heavy-throttle operation leaves the cooling system woefully under-capacity. And this WORKS for just about all cars and light trucks--until something goes wrong.
The solutions include increasing the heat-rejection capacity (such as: bigger radiator, more airflow, more coolant flow) or causing the engine to produce less heat (such as: fix dragging brakes, fix lack of timing advance, reduce load)