IMO, get the most you can afford. You gain the ability to play lower frequencies (mainly for movies) and the power to fill the room.

Not sure what too much money is for a sub... I have a $2000 monster (SVS) in my similar sized room and I am grinning from ear to ear every time I watch an action movie. Do I "need" that much sub??? Maybe not, but it can handle everything I throw at it.

Dave
Audyssey Setup Guide