if you have a look at my room, you will see that it's quite small - around 1500 cu. ft. plus an open doorway to the kitchen = 3000 cu.ft. - and i sit about 6-7 ft from the front speakers.
when i play some demanding movie at Reference Level, the front speakers need around 300 Watts/ch.

gearcruncher, in your calculations, don't forget that cubic feet is the important thing in audio;
sound "fills" a room, from floor to ceiling.
after that, it's distance from the sound source; square feet doesn't come in the equation.