Here's my cents worth.
I am not a chemical engineer nor do I work for an
oil company. However, with some common sense and a few things I know about
oil, I may be able to shed some light.
I know that
oil needs to be hot enough to ensure proper flow and hence lubrication. I also know that it should be hot enough to assist in evaporation of any moisture contamination due to condensation. Those who live in damp climates and/or subject their vehicles to damp cold weather need to be cognizant of an adequate warm-up. Another culprit is short runs when condensation can build up and the temp is not ample to assist in evaporation.
There is no question that the greatest enemy to oil breakdown is not cold, but heat.
I have a fully functional oil cooler with 1/2" AN fittings and lines. I also live in Florida and most of my driving is in 80 degree and above ambient temperatures. My car is also garaged.
Oil pressure is always around 50-60 PSI and I have not had any problems with condensation.
My suggestion, Go with the functional cooler, and use the thermostat if you subject your engine to colder damp climates.