Yes definitely your car is going to run better with a thermostat your car is designed to run at that temperature for maximum fuel efficiency and reduced wear.running your engine cold doesn't give the oil a chance to reach it's specified viscosity and carbon/sludge cleaning abilitys.
If your worried your car might overheat invest in a slimline race fan ,I know from experience even a smaller diameter fan does a better job than the original.you can also fit a override switch (through the factory relay)if you think it might over heat.