1966 dodge dart radiator question

Yeah, I am hoping to install a shroud eventually. I am running a 185 thermostat and never had a problem with overheating last summer. Just a stock 318 roller motor for now. Which brings me to a question as to how low of a thermostat temp you can run? Went with my Buddy to pick up his Ford 331 stroker motor from the engine builder the other day. He told us that a 165 thermostat was all that was needed for summer time. Had it on the dyno. 4 runs , made 426hp and 465 torque up to 7000rpm.