A 140 is too cold.
The engine will only run at or above the temperature that the radiator size vs. load vs. air temp permits - you can't make the engine run colder than these limits allow. If the engine runs hot with a 190, a 160 will do nothing.
The limit to cap pressure is frequently the integrity of the radiator seams, use the highest one you think is safe. Why? Because the water temperature at the exhaust valve is always above the thermostat temp, and increasing the boiling point is the only protection you have against local steam formation.