OK, you did a good and complete job
Have you check temp with an infrared device in several point ?
Keep the thermosat from F/S and indeed check it in hot water to make sure it opens and close.
Have you replace the main radiator or the heating radiator ?
You need to make sure when you put temp max on the dashboard, the infomation is going from the ECU to all components, including heater tap
You may have also some air in the system.
You may have to test the complete A/C system with this kind of tool to make sure the electronic side/ ECU.... is perfectly working:
This is a loan tool which carries a surcharge against non-return or damage
www.flyingspares.com
Giving high level anti pain seems to solve the problem, in fact it does not, it just hide it and make it bigger.
This is why you should digg and consider your issue is not solved, but just hidden behing a hotter thermostat which put the engine in danger.
Even if your car has no turbo, you do not need hot point which can damage headgasket....