If you aren't racing, there would be no benefit to having an oil cooler. If you are prolonging the time it takes for your engine oil to get to operating temperature that could actually have a detrimental effect to a car that is daily driven. Not to mention I've heard a few people lately complaining about fitment issues and leaks from the oil coolers.
I've had the Boss oil cooler on my GT since 4000km and have 17000km on it now. There have been no detrimental effects on the car; the engine heats up just fine; there was little difference that I could tell. I have an Aeroforce Interceptor and can read engine temp, it heats up pretty fast.
The stock oil is so thin it doesn't take much to get it to operating viscosity. That's not a concern. I would think overheating your oil would be more of a concern if you had a choice between the two.
"We are all born ignorant, but one must work hard to remain stupid." ~Benjamin Franklin
2012 Kona Blue Mustang GT
Roush Phase 2 625HP Supercharger | Black OTT Stripe | 400A | 5.0L | 6MT | 3.55 | HID | SP | CP | BBP | EP | RVC
Mods: Forget it .... too much to list!