New thermostats don't fix problems in the cooling system unless it was the original problem. If it stays normal after the cooler thermostat I'd consider your old 195 to be defective. A new 195 would have fixed it too, and a 180 will usually let it run at least a few degrees cooler at most times.
My car has never gone above 205 in the year and a half I've owned it, and I've been in heavy traffic in the hot summer. That was with a 195 and 180 thermostat, either or won't affect the temps in those conditions. Any other condition it will usually run cooler if the system is capable of cooling on it's own below 195 without the fans. (since they will not come on til 212) Generally with a clean system, it should be able to keep it at 190° in normal city driving. I've got a new radiator so that may be why mine runs cool. I've replaced many radiators at work, only to find a huge pileup of dirt, dust and grass on it. And that's between the condenser and radiator. That will hinder cooling system performance quite a bit. The fans would run a lot, and it would probably run at around 212 most of the time.
And I don't think your mpg will ever suffer with a 180, I'm pretty sure that's above the fuel trim adjustments.
