Even most movies don't often delve below 25hz. All of those great sounds in Twister are well above 20hz. I know that there are scenes in some movies; depthcharges from U571, scenes from the incredibles, etc,etc..) that utilize sub-20hz harmonics. I am aware that there might even be hundreds of movies that have bass under 25hz in the soundtrack. There are however thousands of movies that don't do this. And even in the movies that go into subharmonics only a tiny fraction of the movie occurs in that spectrum. I think that the cadence xsub will add as much enjoyability to a system as any of the other subs mentioned, including the HSU and SVS subs. I also recently heard the Bic 12" sub and almost the whole lineup of HSU subs. The Bic will keep up with the STF-2 no problem, I'd rather the Bic by a mile in fact. Don't get me wrong, some of my favourite movies have bass that my sub (or the X sub for that matter) can't get within a mile of reproducing, but no subs in this price category (sub $400 US) can with real authority IMO. Please don't show me charts of SVS hitting 20hz at 96 db or 93 db, whatever the number is guys, you don't need to defend your purchase to me.
Remember to tack on shipping to those HSU and SVS subs as well ebterp. I just think that in the "tight" budget category the better buy is either the Cadence or the Bic offering. If ebterp ups his budget again and can allow for a 12" then I'd heartily suggest the STF3, it's a great sub. I'm sure the SVS 12" subs are great too, but I haven't heard them. If it were me, and I had to choose between HSU and SVS 10" subs, and the Bic and Cadence 12" subs, it wouldn't be much of a choice. Again that's my opinion, and I'm by no means an audio authority, but I think I make a good case for my position.