the jb is a warmer pup to the distortion due to the alnico magnet. most rock bands use the jb, tend to use it in the bridge, dave mustaine used to use it in the bridge, and countless other artists. I got the distortion as it has the ceramic pickup which i prefer. The duncan distortion also adds more mids. Its a slightly less 'hot' version of say an emg 81, without the piercing high end
http://www.seymourduncan.com/comparetones/pickups/34
thats comparing 3 pickups i own in different guitars, the dimebucker is in my razorback, and that really has the high end kicked up, i really prefer the duncan distortion to that, and between the duncan distortion and jb, summat like that youd want to try yourself, depends on your playing, the style of music your'e playing and tone you want.
If that link works and you see the three pups, then there are sound samples of the jb and distortion in the bridge position.
you can still get the distortion sounding warm though,
http://myspace.com/seventhhell (the southern sludge demo) the fizz that ppl have been saying about that mix is due to my actual amp tone and the shit quality myspace does to decent songs!!, not the pup