Ford has a 195 temp thermostat in the 7.3. Some claiming using the 203 thermostat from Dieselsite.com has benefits but I truly can't see how 8 degrees makes a hill of beans of difference, can you say PLACEBO!!
The superduties have a very robust cooling system and to run on the cool side is totally normal. Mne has never reached halfway and that was towing heavy up the mountain in 100 degree weather.
NCH