Which thermostat should I use???

Hello all, I have a 95 Passat GLX VR6. I am in the middle of changing out my entire thermostat housing due to a bad coolant leak. I have removed the cracked parts (entire housing) along with the blown gaskets (engine to housing). My question is this: I will be replacing the entire unit, thermostat included, should I use the stock 180 degree thermostat? Or should I use a lower 170 or even the 160 degree thermostat? What are advantages/disadvantages to each? I drive 140 miles a day (all highway) round trip to and from work and would like to be able to use the A/C a little more without the temperature creeping up on me. With the stock 180 thermostat it reaches over 200-240 some days...Would a cooler thermostat help without any adverse effects? Thanks in advance... Brad