you dont buy subs for a box you buy a box for subs.
here is the EBP Stuff. i was a little off.
EBP - The efficiency bandwidth product, a rough indicator measure. A common rule of thumb indicates that for EBP>100, a driver is perhaps best used in a vented enclosure, while EBP<50 indicates a sealed enclosure. For 50<EBP<100, either enclosure may be used effectively.
EBP = FS / QES
EBP above 70, not too good in a 4th order, stick to ported or 6th
EBP between 40-70 either 4th or 6th would be fine
EBP below 40, probably best to stick with sealed applications
if you want it to work well in a 6th you want over 60. here is a calculator for that
Efficiency Bandwidth Product Calculators - EBP, Speaker Resonance Frequency, Speaker Electrical