under $300 i would have to say the tightest is the x-sub (probably the stf-1 too although i haven't heard it). but, any of the subs you have listed are best for smaller rooms. due to the size of your room i would have to suggest holding off for a few more weeks or so and bumping your budget.
if you get one of these NOW i feel you'll be upgrading soon because in that room you'll be missing out. it happened to me with the x-sub, which is a FINE little sub don't get me wrong, BUT, now resides in my small 10x10 PC room hooked up to my soundcard and an old technics receiver. where it does terrificly because that is the sized area it is built for.
whether you listen "loud" or not, IMO, you will be missing a good chunk of the lower spectrum. you don't have to be a "basshead" to reap the benefits of a powerful subwoofer. i'm not and i have an svs 25-31pci tuned to 22hz. i actually run this sub flat -1 or 2db with my mains and the difference in range between it and the x-sub is amazing. and even on some tracks like WOTW (not my favorite at all but, a good reference nonetheless) it is incredible.
i think also that the BIC will leave you wanting more in the end too.
so i guess what I'M saying is take my advice as someone who's already invested in the "best under $300 subwoofer". if money is at a premium then hold on until you can get a nice QUALITY 12" sub of your choice (svs, hsu, etc. etc.) you'll have less buyers remorse and save $$ in the end. you don't have to break the bank but, if you can stash away $100-$300 more you can get something that will keep you happier for a lot longer in the $400-$600 range.