Potential is almost completely based on displacement. The VR6 is capable of more power then the 1.8t. I know how easy it is to modify a 1.8t up past VR6 stats with a simple chip, but from then on it gets harder and harder to squeeze any more power out. The VR6, with a turbocharger, would demolish most 1.8t's. So if you have limited money to modify, the 1.8t can be made to be faster then the VR pretty easily, but as your money to modify increases, the better and better the VR becomes.