I have a stock 99 foreman 450 S, my buddy has a stock 2005 Rubicon. Side by side he outruns me by about 4-5 mph (48 mph to 52 mph). I'm not sure about how much more top end you get with pipes and a jet kit, but I would think you should keep pretty close to him. I doubt you'd be able to walk away from him, but I could be wrong.