Me neither, never seen a direct link to a data sheet for one of them. AFAIK the magnet assembly is the only difference.
Anyway, next level would be the different magnet ingredients.
Note that discussions about alnico vs. ferrite, and their impact on sound can get very passionate here...
Facts to start with:
http://audioheritage.org/vbulletin/showpost.php?p=37039&postcount=1
and the designer on the subject:
http://audioheritage.org/vbulletin/s...2&postcount=29