My quick 2 cents. In a small space you will probably not notice very much difference between quality subs. Having said that, there would be no disadvantage to getting the larger sub with the exception of cost. You can tune it so that it won't overwhelm you or your neighbours.
The fact that the VP150 is exactly the width of the TV is to your advantage. Assuming that the tv is black, you won't find that it stands out. My wife is addicted to those home improvement shows where the first thing they do is hide the sound system. She doesn't even notice it.
I have M3 fronts, VP150, and QS4s. I went with the M3s alone for about 6 months before I added a sub. In my experience there was no music I threw at them that they could not handle on their own. My listening space is about 12 by 12, although it is completely open behind the sofa. They filled that room with wonderful sounds. The sub is there purely for movies and to scare the cats.
