I wouldn't be surprised if the Q950's give them a run for their money in the Bass department.
My Q750's measure pretty much flat to 40hz with usable output to 35hz (attached measurements)
Feedback from Q950 owners is usable output down to low 20's but i haven't seen any measurements to back that up yet. I wouldn't be surprised if the Q950 bass performance is similar to the SVS Ultra towers.