No so sure about the M5 clutch.. yes.. it works wonders in a car that is putting a lot of HP down.. but he has a 97 M3.. it would take a lot of work to push 500hp... which would be the only way that said clutch would be of good use...
AA Tuning makes great clutches... I would check around though... read some reviews... SACHS makes a good heavy duty clutch kit for our car...
www.turnermotorsports.com sells them... good stuff there... they sell a few others... search around.. and call a few of the tuners.. they dont mind pointing you in the right direction...
Good Luck,
Les