31 km/h. If the brushless have the torque to get it moving, it will be fast.
With the right speedo, you could have a suitable setup.

But with a Z90-12 secundary gearing (18.75 -1 ratio total) top speed will be 27.5km/h
The max advisable secundary gearratio is Z96-12 (20-1) and you still have 26 km/h

I know what I would choose.