A couple months ago I bought an '06 YZ450 that was a stocker with the Scotts submount damper system. Over the course of the next several weeks, I added the following (just because I could and I wanted to ): Zipty carb mod 'kit' MRD-Racing full exhaust system with S/A (S/A req'd here) IMS desert tank New chain & gearing on the way - 13/50 Cycra pro-bends Hour meter Gripper seat cover on the way Rekluse z-start pro Stainless oil filter After all is said and done, and finished bolting stuff on, my favorite mod to my surprise is the Pro Moto Billiet kickstand. I use it all the time. I'm getting old and tired when I ride. I have not been able to get off my bike during a break since 2001. Excellent quality and function. I think the best performance mod is the Rekluse since I ride the tight single track trails here in AZ. It has allowed me to lug (ahem...cheat) up places I had no business going before. Its also helped me in the berms because you can stab the rear brake without thought of the clutch and it doesn't stall. My $0.02 worth.