I've changed from spool to geardiff with 200.000 in it, And noticed a slight difference in onthrottle corner exit. The car has a bit more steering and feels less stable. Also the brake is a little less "hard". But overall you have a bit more cornerspeed, and you're front axles wont wear as hard, as with an spool.
Hope this helps
Sponsored by: Schumacher Racing and Dualsky
Supported by: Shepherd Benelux and Thunder Tiger.