Which Rel sub for Audio Physic

I am trying to add a sub to my system comprising AP Sparks and a Jolida tube integrated (1000rc). Would appreciate recommendations, Rel has so many product lines, T, R, B and Reference.

I would like to get the biggest bang for the buck, $500-$700 used would be ideal.
size of room is one of the most important factors. I went from a T-2 to a B3 with good results in a 12x12x9 room.
I ended up getting a Rel storm iii and it works great. Got it for around $850 used.