With a lower temp thermostat you are going to gain a little power, i mean little because the engine is going to be cooler so the air and fuel mixture will be cooler. Cooler air and fuel means more can be packed in the combustion chamber. more fuel and air in the combustion chamber means a bigger boom which gives you more power. This will hurt your mileage a little bit.
as for if it is better for the engine or not i think it is a little better.
it helps a stock engine to get a re-tune. the factory is very conservative in their tune and does not tune it to run at its peak potential. since it is fairly stock i think you could get a internet tune to work pretty well