Simplest solution if the speedo's cut out on overcurrent, less V.

Something I think will be needed whatsoever.

Those cheapo's run a lot faster than a Graupner Speed 900. I messured them 11000 rpm @12V

11000/12=900 rpm/v
900*14.4V=12960 rpm

Gearratio 5-1. 2592 rpm on the wheels.

0,125m*pi*2592= 1017m/min=61km/h