So, I think your issue is the rpm you've chosen to calculate by. A free spinning CIM with NO load spins around 5200rpm. A CIM under load (like on a FIRST drivetrain) only spind sup to about 4500 (sometimes a bit more or less depending on the weight of the drive system). A good place to start calculating from is 4000rpm, as your max speed will end up closer to what you want it to be, and you won't have to do a crazy amount of math to factor in drag and so on.

As for the 19fps, that's a little quick, but controllable. The main issue you'll have with that speed is acceleration. Add another motor to the gearbox, and you'll find your acceleration increasing a decent bit.

Good luck!