radiohunter, I upgraded to a DIY 18" Dayton HO. Was thinking of jumping to a higher quality ID sub, but took the leap into the DIY realm.
That Klipsch RW12-d would outperform the Bic F12 and Polk 505 combined(below 30Hz and possibly above 30Hz). For $279, you can't go wrong. I'd jump on that if I were you. If I only had $200 to spend I'd have no problem going with either the Bic or Polk. It would come down to which you think looks better.