AutoX car will need to be very nimble and change direction really well so low end response needs to be "snappy" and the chassis will be set up so the car is "looser" due to mass of a Mk3 you'll probably be sliding it a lot to make it turn quickly.
A track car will probably be the opposite of the above as any sliding will destroy tires quickly and more top end from the engine will be needed.... very different set ups as I said, somewhere in the middle will be okish for both but you're going to have your ass handed to you by a well set up lesser car on either track.