they have dealers everywhere i can think of. heres their pinion chart
http://www.robinsonracing.com/catalo...n.html#one-mod
the 6s seemed to crazy for me but if i try the cd like you did then it might be nice. the 5s is perfect for my driving and where i bash it. crasy speed and long running with 20t on a 44t spur still. its stock flux parts but used the hd trans gear inside not the speed one