Jim, I use the Racing Beat Main pulley which is suppose to reduce my
alternator and water pump  rpm by 20% over stock.  Then I also have the
Racing Beat Alternator Pulley which is suppose to reduce the alternator rpm
by 20% .  So with both my alternator is running approx 40% less rpm than
stock.  Still provides plenty of power for all my crucial systems as well as
two landing lights, strobe light, Nav lights, pitot tube heater and charges
two Batteries.  I am hoping that by derating the alternator such that it
will last longer.

Ed Anderson