I have the Strata III, I have heard the Storm, both are great. I would use the Storm in a bigger room than the size you have. They main reason to have two subs is to eliminate standing waves, so the effect of two Strata III's or two Storms would not be very different. One Storm is not better than two Strata III's. Unless you want to wake the dead, one Strata III is plenty. Good luck.
REL Storm III or Strata III
I've read great reviews for both subs. I'm looking for the best complement for my main speakers (Thiel 22's) and listening room (15x16x7). I'm runniing plenty of power to my Thiels (400wpc) and they sound great. I am planning to add a sub primarily because of a recent addition to Home Theater but also want the best audio for my two channel. I'm leaning to the Strata III because of what I've read, they have a slightly tighter sound with no ill effects of a ported design to that of the Storm III. Also if I come to the conclusion that the Strata cannot kept up with my Thiels, I could always mortgage my home and get a second Strata. I really don't want to go that route if the Storm is all that I will ever need. Anyone who as owned or heard both in the same listening room, please give me some feedback. Thanks