cpplain, i can tell you from my own experience, room size is a HUGE factor.. the current house i am in resulted in my upgrading from a single 5 channel amp. to 3 separate amps.. My current Great room is 2,400cu/ft.. But, since it's a Great room it opens to several other rooms within the house...
I went from 135W per channel, to 250W per channel... When i listen to music, the average sound level is about 95/96DB.. Movies are about the same volume. So, pretty close to your stated 100DB. For a given amount of power the room size will play a role in the over all DB level within the room.
Others will chime in as well. hope this gets the conversation rolling.
