In the bass region, the room dominates the low frequency presentation. Relatively minor differences between quality subwoofers pale in comparision to the large peaks and dips that the room imposes. So my suggestion is to consider the room to be very much a part of anything you do in the bass region. The approach I prefer is distributed multiple subwoofers, as advocted by Earl Geddes and Todd Welti (leading researchers in the field).
I suggest three or four small subs, with 4th-order low-pass filters that can be set as low as 30 Hz, scattered asymmetrically around the room. Each will inevitably generate a unique peak-and-dip pattern at any location in the room, but the sum of these multiple dissimilar peak-and-dip patterns will be smoother than any one of them would have been. And "smooth bass" is "fast bass" - it's large, usually room-induced peaks in the bass frequency response that make a sub sound "slow".
Duke
I suggest three or four small subs, with 4th-order low-pass filters that can be set as low as 30 Hz, scattered asymmetrically around the room. Each will inevitably generate a unique peak-and-dip pattern at any location in the room, but the sum of these multiple dissimilar peak-and-dip patterns will be smoother than any one of them would have been. And "smooth bass" is "fast bass" - it's large, usually room-induced peaks in the bass frequency response that make a sub sound "slow".
Duke