Any modifications that improve breathing will start to take effect at around 3200 RPM. If the photopost link starts working, you will find that, on the many dyno charts that have been posted, the torque curve is quite flat on a stock bike. With improved breathing, the torque curve starts angling upward at 3200 (the speed where the carb slides start to open) and the power curve follows it.
Unfortunately, this is mostly true of the older engine. The 865 needs better exhaust valve timing to get the full effect of intake and exhaust mods.
Anything that increases air flow through the engine will require rejetting to give a corresponding increase in fuel flow.
