[GTRaptor]

I think many of us think of thermostats as smaller is better (up to a point).
We all go and swap the stock 192° for 180 or 160 units thinking it will drop temperatures considerably.
Others go and get rid of it completely.

What is really the best thing to do????

The cooling system is closed, rarely you need to add coolant if everything is fine, the coolant just recirculates endlesly until is time to renew it.
If by some reason the pressure rises, then the excess pressure is released by the radiator cap into the reservoir bottle, then as the coolant cools down, the coolant in the bottle gets back into the system.

5.0s and 4.6 run at high temperatures, between 210 and 230 °F.

If you know some basic thermodynamics you will agree that the system is as good as the ammount of heat that the radiator can disipate in a full cycle.
The engine will heat the coolant up to a certain point, no more, no less. That heat has to be disipated by the radiator in X ammount in order to keep the engine at a certain temperature.

So, if the engine generates X heat, and the radiator dissipates some of it to keep coolant at a constat temperature, why does one need a thermostat?????

It really has nothing to do with the time the coolant spends in the radiator, since it is a closed system, the coolant recirculates endlessly, so the coolant has a "constant" chance to cool down.

The reason why thermostats are so important is because when you remove the Tstat, bubbles have a big chance of forming inside the engine coolant passages. Just imagine the heat that the coolant takes from the engine, without a thermostat those chances increase.

When the thermostat is closed, the engine side is completely pressurized, meaning, the coolant has a lesser chance to boil because of the pressure, and also theres less chance for air bubbles to appear.

The Mustang cooling system is pressurized at 16 psi, thats not much pressure, but thats on the radiator side, on the engine the pressure is much greater. The higher the pressure the higher the boiling point.

The thermostat releases that pressure in a controled manner into the radiator.

The theory says that if you get a lower temp TStat, pressure will increase, and hence, you will need a higher pressure radiator cap.

Some manufacturers use completely closed cooling systems, those operate at much higher pressures and lower temperatures
Some liek VWs get coolant temperatures of 190 degrees without a problem.
Why FORD uses a lower pressure system?

MONEY...it is more expensive to build a high pressure system, so we are stuck with 16psi.

So what do you do???
If your car generates more heat due to increased combustion pressures, a SC, turbo, etc. the best thing to do is to install a more efficient radiator to get rid of the extra heat.
An oil cooler is also a nice addition, and a cheap one compared to a new radiator. This is the best route if your engine is not extensively modified, will reduce the engine heat and with it, coolant temperatures.
If you go smaller on the TSTAT, stay with 180 or stock units, a 160 or no thermostat will increase system pressure and chances of failure.

Also make sure you take out the underhood heated air, that creates more pressure on the cooling system. Cowl hoods, functional scoops and even front spoilers help get rid of it faster.

Well...will love to elaborate more..but have to get back to work.