This is my 4x4. Build specs;
VXL 6S 2200Kv motor and esc, Robinson racing hardened steel 20T pinion and 50T spur, H-R slipper eliminator, HD diff cups, steel helical ring and pinion gears, XO1 differential guts, traxxas steel splined CVDs, techno big bone drive shaft, 2255 servo, aluminum...
Go LCG. The way the servo is tucked away protects it from impacts. My personal opinion is to upgrade to the traxxas 2255 servo; the high torque/high speed metal gear blue servo. I got one on my 4x4 and love it. Then get the aluminum servo arm and aluminum bell crank.