How to find the right gear ratio ?

Hi all, recently I've swapped the Castle Neu 1520 for the big 1717 (thanks to Castle sale) and I wonder which is the best gear ratio to use with this kind of motor.

My savage (here the gallery) is a bit heavy and has the tranny with the Flux standard gears (not the High Speed Idler gear) and bulletproof diff gears (9 / 29 ratio).

At moment I'm using a 47 tooth spur with a 25 tooth pinion, for a final gear ratio of 13.42, but I can't figure out (before testing) if I can make the ratio lower assuming the amount of torque the 1717 can give out.

Keep in maind that the FLM Forward Tranny Chassis doesn't allow for many combination of pinion and spur due to the space I need to have within the chassis to mount 6s Lipo

What do You think ? Am I lower/high on gear ratio ?

By the way, here is the custom motor mount I've built to fit the 1717





As You can see, I have made the mount higher to have the motor shaft on the same horizontal plan of the spur axle. This allowed me to maximize the distance between the two shaft and, hence, having the motor mounted as much outer as it possible with respect to the chassis, so to have enough space for the batteries

Thanks, Andrea.