Andy Baker (Andymark) has a great power point on
basic drive trains. There are many others presentations. Google is your friend, One of the big advantages of 6 wheel systems over 4 wheels tank drive is that the shorter effective wheel base makes it easier to turn. That is assuming that it is set so the robot is mostly supported by the center and one one set of the outboard wheels. Pneumatic wheels are going to make proper set up more critical. Any tank drive has to scrub the wheels to turn. High grip wheels are going to need a lot torque to turn from a stand still and the turn is likely to be a little jumpy. This is one reason many teams use omni wheels on the corners.