Well, since I'm down here in Texas and daytime temps are 95 to 110 degrees and evening temps in the mid 80's. Even with a 160 degree thermostat my car runs around 175 to 180 when cruising and gets up to around 195 in stop & go traffic. I have a stock Six Pack Challenger R/T with a #956 3 core radiator - 26 in. wide. My car however is 4.10 geared - 4-spd.
Either way I think you'll be O.K. so if you feel more comfortable with a 180 degree thermostat then go that way.
As for it hurting a motor to run 15 to 20 degrees cooler I don't think that would be the case. As for making more power, I've always run a quicker time at the track with the engine at the 150 to 160 degree range vs. the 180 to 195 degree range. I have never done a comparison on a dyno to see what temp range makes the most power.
