I agree with John, but take a look at the 20-39PCi. It gets down to 20hz, but you give up a bit of headroom; not that you are likely to need the missing volume unless you will be commiting "death by LFE" . I felt I got a bit more benefit by going lower (at any volume) than bu having more headroom I wouldn't need/use.

What you really should do is call SVS and have them talk you through the decision - great folks.