I have been running 9886 pipes for years now and it works great at my track. My track has as a smooth and flowing layout like Rich described. We don't have many areas where the car comes to a complete stop (none, really) - the car will will definitely drop down into first gear in most of the corners on the track, but the car never slows down enough so that the clutch disengages.

That said, I'm going to try one of the 2013 Pipes after my current set of 9886 pipes get all banged up.