There is such a thing as too much flow. Unless the car is modified for it, running with no thermostat can reduce the coolant's ability to conduct heat from the cylinder walls. Your gauge may be showing lower coolant temps, but your combustion chamber temps might be higher. This is caused by too much flow through the heads (with no tstat) creating cavitation and excessive turbulence in the water jacket. That reduces conduction from the metal to the coolant since the coolant moves through too fast.
This is actually one of the harder parts of tuning a custom liquid cooling system in other industries and hobbies. Too much flow and you'll see the temp rising on the item you're trying to cool. GM already calibrated the system with a thermostat, and I'm not going to be ripping it out thinking I know what I'm doing.
