Although I'm new to this forum, I think you need to keep in mind the "needed" power verus power gains. When you have an application that you are drawing every last bit of power out of an engine, mods like exhaust and intake can make a difference. I think MOST of the time we don't use all the power our tractors have, and the times we need peak power are not that common. If you have an application where you feel your engine is lacking, maybe an intake or exhaust mod might help, BUT, I personally would not want to take the risk of goofing up either reliablilty or durability for the sake of a few horsepower that I might only need once in a blue moon...
Just my two cents worth....
Todd