The JL 8" drivers have a lower FS and also greater excurison capabilities than the 10" or 12" drivers in the same range.
The 8" driver has a resonant frequency of just below 40 Hz the big difference in output level is due to the cone size and resultant piston area - hence the greater efficiency of the larger drivers.
I run the 8" stealths up to 80Hz, but with a steep 36dB slope on them to stop the image of the bass drifting rearward. If using a shallower slope around 12 or 24 then I'd go no higher than 65 Hz with them. But they'll reah all the way down to mid 30Hz with no trouble.