Sx will die if you made it road legal. I have an xc on the road that is my backup bike and sx as race bike. Had a drag race with a 505 at the weekend on my xc and was only about half a bike length behind after 150m. That was with road gearing and 20" tires vs 18s. All my xc has is 540 kit, 12.5 piston, 806 cam and an sx slip on. I bet you wouldn't be that far behind with just the piston and cam. Got a 833 cam (more top end) to go in at some point and the 806 may be up for sale if i prefer the 833. I'm from scotland so ill pm you my number. Feel free to give me a shout tomorrow if there is anything you want to ask? Michael.