As I said before, and I will say once again, the rated opening point of the thermostat establishes the MINIMUM operating temperature and has ABSOLUTELY, POSITIVELY NOTHING TO DO WITH THE MAXMIMUM OPERATING TEMPERATURE unless it malfunctions by sticking closed or not opening all the way.
Whether you have a 71, 79, 82, 87... whatever, themostat installed, once full open, the temperature will continue to climb in hot weather stop and go traffic until airflow through the radiator is increased by the fans or faster vehicle speed.
The thermostatic clutch on the engine driven fan tightens at 100C, but idle speed doesn't create much air flow. When the electric fans engage at 105C, the airflow through the radiator is substantially increased, even if the vehicle is stopped, and should quickly drop the temp to the fan cutoff point.
If your temp gets to 110C you should check for proper operation of both the engine driven fan thermo clutch and electric fan operation. If this temp is achieved with proper fan function then radiator tube deposit buildup is possibly to the point where the radiator cannot keep up with the heat transfer requirement no matter how much air is pushed through the core.
Water flow tests mean nothing. The only way to determine if the tubes are clogged is to remove the end tanks and inspect, or just replace the radiator if all other cooling system functions check out as okay.