Was watching an electric bike design summary on YouTube and was presented with a anecdotal golden-ratio for motor kV rating and pulley ratio, in the attached photo.
Going off of my board, motor kV x motor pulley / wheel pulley * wheel diameter = 8000 for a board that can go a little over 25 mph comfortably and has good torque so staying around there would likely be good. I would however second what Monomas11 said and use an esk8 calculator like this one: http://calc.esk8.it/