I just put in the dealership 87C and it starts regulating at 87 and stabilizes at 90C (194F).
I only changed mine because after driving indefinitely, even up mountains, I could not break 74C coolant temperature. I verified this with a thermocouple and a meter, and the ECT probe is accurate. It turned out that I could put a glass in the microwave, and with the water at 78, the valve would open, and not fully close until below 73C. I guess after 9 years it got tired and started regulating at lower and lower temperatures.
For some reason it must have been close enough to not set P0128 coolant valve regulation limit not reached. I only noticed when I wanted to see how hot I could get it under full load and 77C seemed really low for going up a 7% grade for several miles.
Maybe now my fuel economy will go even higher (fat chance at 56.1/70MPH)
I don't see why you would want to go any higher than the normal setting though. 90C was probably chosen as the nominal temperature to keep combustion efficiency as high as possible without compromising lubrication, cylinder head cooling, or maybe even emissions.