I have a SVS pb2plus sub and I think it is awesome. It is quite an overkill for my room dimension. This just means I just turn it down substantially. The addition of it to my system was tremendous. In HT use it provides an experience like non other.
As an example I went to the public movie theater and watch Ruddik (Vin Diesel). I paid particular attention to the audio during the movie. I now cant wait to purchase the dvd so I can hear it on my system. It is funny that movie theaters no longer provide the awe inspiring experience they once did. My expectations have obviously raised dramatically.
Also keep in mind that delivery from SVS, especially on that model, is usually a few weeks out. It is a long few weeks wait. Well worth it, but my suggestion would be to order it before you are ready and pretend your still thinking about it