I really don't think the 500 would be overkill in any size room. From a volume capability perspective, yes, but much more important to me is how low a sub plays, and the 500 plays lower. Fred's response a few posts back is right on the money. You could put an EP350 and an EP500 in an 800 cubic foot room and still get the benefit of the lower extension of the 500 when watching movies.
If you have a moderately sized room, I'd make your selection between these two (or the competition) based more on how low a sub can play with flat response than how loudly it can play. If you're primarily a movie watcher, the extra punch in the low frequencies will be well worth it.
Jason
