I have an XSub box and amp. Contacted PE, they recommended, IIRC, the 295-185 driver as the best match, most likely to duplicate the Cadence specs. But, he didn't think it could go below 30hz in that box with a 7.5" port, tuned to 50hz. PE's guessing that the amp has some built in EQ to achieve 25hz.
I've been looking at other driver's as well and it's no sweat off my nose, because I have a working XSub. But I wouldn't risk putting an upgraded driver into a working sub, if it wouldn't provide better SQ or extention. I'd get another sub.
edit.
According to craigsubs numbers, 2 Xsubs will give you ~ 99db @ 25 vs. 1 PB10 102db, not to mention the < 25 output.