In your size room an EP500 should be more than enough. I had one temporarily in my room roughly 20x10x7.5 and it pressurized the room.
Just to let you know though, when I was at Axiom and we were listening to their set up (80's & 50's & QS8's) we had both the EP500 and EP600 on a switch box. To me and my buddy there was a very noticeable difference with the EP600. The thing is a beast.
Is it worth an extra $600? If you are already buying 80's, VP150, QS8's and at a minimum an EP500 then YES. However, I would also suggest like above on getting the EP500 first and trying that out. You can always have it sent back to Axiom to trade up to the EP600.
