I have a 4.10 in mine LOVE IT! ..top speed is still good if you can do 6,500 rpm.
but if your car is an "E" then i wouldn't go higher then 3.73
And about the Spider pin thing.. yeah i blew the old diff that way.. but the 325ix diff seems to be much stronger. Either way bmw's arn't made to rip gears, So i would avoid shifting very hard
E30 Stuff For Sale: Clutch Fan and Shroud, 4 Pack Ignition Coils, ATE 750il MC (New), Offset Trailing Arm Bushings, m42 Valve Cover (Clean), M10 Engine Mounts (New), M42 Injectors,