yeah i was running 28 mudlites, and the stock clutching is the best for speed as far as i found out, but i have to ask if your running 28s why you are worried about top speed, i can tell you from personal experience the 28's are hard on stock tie rods, and in high gear on takeoff with stock primary spring gets hard on the belt, easier to glaze a spot. anyhow if you ever want to clutch it for low end grunt go lime green secondary, but it tops out around 55