I have center torsen with 52t spur and pinion is 14t, front and rear diffs are stock.
Well those rims have been broken because very bad landing...
Take a look at my thread for more infos
My Hobao Hyper ST Pro conversion.
Btw. There is no need to make any new holes to chassis, you can manage with stock holes, even centerdiff can be flipped, you just need to raise Mikes motor mount for 1mm, to make acceptable clearance.
For 6S batterys (still coming), im going to use 11t. 52/10 is lowest gearing you can go with 36mm diameter 80mm lenght motor, without need of modification to center brace.
This calculator is very helpfull, when determining lowest gearing.