Engine overheating
Thermostats only set the minimum temperature that the engine will run at, if your cooling system is adequate then this is also your running temperature.
So putting a lower temp thermostat will only lower the engine temp if it isn't already having a cooling issue.
Removing the thermostat and getting a lower temp is an indicator of a flow problem, but it could also mean that your radiator has restrictions in it and needs more flow too cool.
A good flush never hurt anyone, and check your plugs for running too lean or rich.
A high flow thermostat may help also.
good luck.