I put a 160 degree in when I first put my tractor together. It ran okay, but not right. The other problem is that it sooted really bad. My exhaust is vertical and I always had the stuff on my face and clothes.
I run the hottest I can in everything else, so I switched it out for a 195 degree. It runs much cleaner, peppier, smoother, etc. The only downside is that I don't really work it hard enough in hot weather (or any weather) to ever get it to set on 195. It swings from 180 to 195.
I suspect when the thermo opens, the cold water of the radiator causes it to slam back shut. It creeps up to 195, then drops fast to 180 then begins its slow climb again, over and over. It still runs rings around the same tractor with a 160 degree thermostat but the temp swings drive me nuts! The tractor is a 1959 MF65