I would basically keep around the same estimates on our site (3000 cu ft). Though that's a very basic guidelines as there are many other variables that determine which sub would work best. We've had people that had a VTF-15H in a 2500 cu ft room and felt they needed two to meet their output needs and we've had ones that had an STF-2 in a 6000 cu ft room and that was enough for them. It just depends on your listening preferences, placement, openings, etc. Do you have a room diagram for both of those rooms?