Pinionsize, help please.

long time lurker, first time poster actually. But thanks ^^

Wheelsize is standard Slash. 7.4v 5000mAh 35c batteries and a CC Mamba Max Pro. Speed is not the goal here, I want durability. Racing without having things overheat and die on me.
Why two diff ratios...well, I use a Revo diff up front and a Wheely King in the rear (Hardcore rear axle), but since I run a center differential it should work out fine. I can't fit a WK diff in the Revo case and a Revo diff will not fit in the axle. have tried to fins some gear with the same ratio (37/13) for the WK but no luck so far.

Will take a looksie at the speed calculator. Thanks!