I was doing speed runs with the rustler (same transmission) geared 19/54 with a Velineon. You should probably go with a Jato 32p spur (which will fit fine on your slash slipper clutch). Then go with a 17-19 tooth 5mm 32p pinion depending on whether you want 42 or 46 mph.
I run Mod 1 gearing in my VXL ruster using a Revo 40 tooth spur and a RCM 16 tooth pinion I prefer it over the 32 pitch