Well I finally rode my 426 yesterday after doing what I would say is the best mods ever. I put the front end off an 06 yz450(DH1 clamps and forks with 1 step up stiffer springs) and lower IMS
pegs(im 6'6"). The new clamps moved the bars up at least an inch.The bike is a different animal all together. I use to have a lot of fun on this bike but now it feels like its part of me. It turns 10 times better and jumps 10 times smoother. Just these mods made my riding progress a ton over night, I feel much safer and confident which tells me how important it is to make the bike fit you.
If you have a 426 I highly recommend 06 or newer front end and if your a tall person try the lowered foot pegs.
Oh yea I had a gold valve
put in the rear a few weeks ago and that made a huge difference as well.