whats the best thermostat for /6

Took the Valiant out on a road trip the other day and the temp guage ran a little warmer than I thought it should on the expressway. It ran a little past the center on the guage. I don't remember changing the thermostat when I had the engine out. So I looked at them on the parts website and it had a 160* and a 180* thermostat. It is a /6, 225. It has a new radiator and all so I am going to change it before the road trip down south. I was thinking that since the car isn't ran in the colder weather about going with the 160* and it should run a little cooler. What do you guys think. Bill