Steam radiator valves shouldn't hiss if they are not leaking. The problem with it being too hot is that wherever the thermostat is located, it's cold, and so the heat keeps running until the temperature is right where the thermostat is. Everyone else on the upper levels, away from the door drafts and the thermostat, gets parboiled. My old church has a steam boiler, and by the time the downstairs where the thermostat is gets comfortable, the people in the upstairs rooms are opening windows.
It might be worth trying to partially close down the valve to your radiators, so the steam can still come up but not full force.