Suspension is the anme of the game
Frankly, I'm a little amazed at how many KDX owners ignore their suspension for engine mods. The MX Tech treatment will make you faster no doubt about it. It really helped me and I can go faster with less effort now. I only have a Rev pipe and airbox mod on my bike and I am happy with the amount of speed it can generate. I do confess that I have some Boysen reeds to install but the biggest improvments have been the MX tech and then the Rev pipe. Having a fast bike you can't control just means hitting things harder. I am impresed with the new re-valve and font fork springs. The bike steers better, enters corners smoother and leaves them faster. Nasty trail conditions will not throw you about like on the stock bike. It IS NOT CHEAP though so be warned. I feel the bike is safer too.