Big Subs: Worth it for "sub"-reference listening?

[McPanse]

I'm looking to replace my Cambridge Soundworks Newton PS500 8" dual driver sealed sub with something bigger and better.

I'm leaning toward an SVS PC-12-Plus for my home theater, which takes up half of a 26' x 16' x 7'8" in my finished basement.

I don't do a ton of reference-level movie watching -- I tend to keep the volume down in the 60-65 dB range.

What does a sub like the SVS PC-12-Plus bring to the party when listening at these more moderate volumes? Should I expect it to do something my 8" sub does not?

Anybody have any experience upgrading from a starter sub who can share their impressions of what their bigger, better sub added to their music and/or home theater experience when the goal was something less disturbing the neighbors with an oh-so-real T-Rex stomp?

Anybody find that their bigger,better sub produced more boom and bass then you wanted to feel or hear?