On LEED buildings I tend to provide 140 EWT, but I did a two pipe system for a dormitory as low as 110 EWT. As long as your coil can meet the load of the space, then from an energy standpoint, the lowest you can go the better.
140 EWT is a good number. It allows the boiler to work as efficiently as possible (if it's condensing) you can put a larger delta T on the coil, and that in turn can decrease the size required for the circulating pump.
Lower water temperature can be done, but why? Max out the boiler efficiency.