i would tend to agree that a well built 400ex in the woods wont be a whole lot different than a 450r if you arent racing against them.

good suspension, a torquey motor with some good cooling mods to keep it from getting warm and heat soaking, good tires, and a good rider will run well in xc.

what do you have done for mods to your 400? are you running with 450s in the same am class? how are doing in comparison to a 450 in the class if you are?

steve