Cab options for Sub1500?

OK - I've run some numbers for the Sub1500, with the main requirement being the smoothest, most solid 40hz for bass guitar - I really don't need any lower in this case, (unless I put them in HT subs...). What I found is that if I tune a 2.4 cu.ft cabinet ('currently have one) to 31.5hz I get a virtually flat curve down to 40hz. Is there any advantage to building a larger cabinet, other than extended bass response below this?

Below are four curves. First is what the programs calls "optimum" for ported at 1.6 cu.ft, next is what I came up with at 2.4 cu.ft., third is considered "optimum" sealed at .84 cu.ft. (??) and last is 2.4 cu.ft.sealed:

http://mark8.org/users/johnaec/Sub1500-curves.jpg

Running the curves for 4 cu.ft. and 6 cu.ft. gives me the option of putting a "bump" in at 40hz, which I don't really need, other than requiring less power for 40hz. Is there something I'm missing, (not counting a 40hz bump and extended bass), or will a 2.4 cu.ft. cab realistically get what I need?

Thanks for any opinions, suggestions, etc...

John