It's only an 8, but its plenty loud for me. In my opinion, it would be difficult to get enough airspace for a W7 ten without extending futher towards the front of the car, or spare tire location... but I'm sure it COULD be done.

Mine's pretty similar to that one, might go a bit more into the spare tire location, but not much.

Why would I want to add polyfill though? I think I'm right about at the manufacturer's recommended size.