I have just completed building 6WD by follwoing the tutorial here.
1. 200rpm 12v DC motor Max stall current: 300milli amp and normal current :60milli amp and 2kg torque each.
2. 6X125mm Off road tyres
3. 12v battery with 4.5ah
4. L298N Motor Driver with Max 2amp output.
5. Aurdino Mega to control the drivers and aurdino UNO for transmitting wireless signels to Mega.
what i notice is that the vehicle with PWM from 150 to 255 its able to move forward and reverse with out any issues.