Based on my what I could tell the speed is very close to 13/90 with the 4600. Maybe the car is little faster with the vxl like the calculations should indicate but not much difference.
Oh well, temps were back up outside today amd I was able to get the vxl motor up to 200 degrees after a couple 15 minute non stop runs using the 19/90 combo. Will try a 16t to see how it does.