i have both and they are diffrent bikes. the power of a shee is sick!!!! high maitenance, if you dont mind working on it then go for it. it seems like somethings always wrong.but is always easy to fix and cheap.stait line - you cant beat a shee.

i have a kfx-400(z-400),it has a little work done and is quik ,but still not the power of a yfz. its my fun/trail bike. i love the power of a shee,but id get ride of it before i got ride of my 400. im 28 so my riding style has changed. when i had my 96 shee in 97 id probably get rid of my 400 first. z-400 best trail bike out there and alot of hop ups.

if i was you id go yfz and have the best of both worlds(but no reverse hehe)

 

yeah, i was reading up on the yfz 450, and now im changing it from z-400 to yfz 450. lol

i ride my brothers 400ex a lot and i've gotten used to not having a reverse