RE: upgrading servo's
Traxxas 2055 is a good compromise between the 2018 and Hitech 645 here is the specs, this would steer the 1/10 model very well!
SPECS: Length: 1.6" (40.5mm)
Width: .8" (20.5mm)
Height: 1.43" (36mm)
Torq: 80 oz/in
Weight: 1.58oz (45g)