Personally I think you may be better off getting a good WR 450, newest you can for the best $$, in the best shape, put in Hotcams, a exhaust/pipe, and jet it correctly, or go with a JD Jet kit, and call it a day, stop working on it, and go out and have a blast. That being said, I have never ridden a 400 or 426, but I can't see them having more power the a equally tweaked 450. that is what i was thinking before i ever started this thread. but then i started thinking they had to of changed stuff and would the changes be better or not? for quality and the way i like my bikes. and a spec sheet wont tell me every thing i want to know. the guys riding them will find all the problems one mite have vs the other bike don't. stuff like that. i guess you could say im trying to learn every thing about 3 diffrent bikes in about what 10 15 diffrent years all in one thread. lol but hey im learning alot more on what i want and also making all the other threads i read make more sence.