whats the best thermostat for /6

Well, it will open and may cooler when at idle and low speeds, but that may not be good for the engine to reach a good operating temp. Too cool can cause sludging etc. As noted, it won't lower the temp of a too hot system. I would stick with the 180 and check the system for accuracy. BTW, interestingly, 160 t'stats were used back in the olden days for the old alcohol based anti-freezes.

Your temp gauge may or may not be accurate, but a little past center is just fine in this early summer weather. You can get a good check on the gauge by putting meat thermometer in the top of the rad with the engine warmed up and the t'stat opened. Or borrow an IR temp gun and look at the top tank of the rad and t-stat housing.

I have also calibrated the resistance of the temp sensor in a pot of hot water at varying temps, and them checked sensor resistance in-engine with an ohmmeter when the engine was hot to get really accurate measurements.