Axiom Home Page Forums General Discussion Technical Questions EP400 vs. EP500: really a big diff?

I'm deciding between an EP400 and EP500 for a mostly-music system in my home.

The room is about 410 sq feet with 8' ceilings, but everything is open in this home and the total area is about 1100 sq feet.

I know Axiom says the EP400 is meant only for small rooms such as single bedroom or den. But the V4 specs indicate only a 4 db difference in maximum room SPL. As I understand it, that would not equate to a very large difference in maximum *perceived loudness*, much less than 1.5x if this is correct (http://www.sengpielaudio.com/calculator-loudness.htm).

So, since the much smaller cabinet would be much appreciated, why is the EP500 considered so much more capable?