I think it depends on what you ride mostly that should be the deciding factor. The 450's are generally aimed for track usage, but can do other stuff, e.i. Dune, trails, flat track, gncc. But out of all of those styles of riding, for the most part they are built with riding on a track as a main area of expertise.
The rappy 700 which runs for a similiar amount of $'s to the yfz is generally the trail counterpart to the yfz. It's mostly geared towards agressive trail riding, and gncc. But again it can hold it's own on the track, dunes, and other places.
And even if you wanted to save a few bucks you could pick up a rappy 660, just be careful of the 2001's as they had tranny problems.
If you have your heart set on one of the 450's you have to look at it logically. Your going to be dropping a decent amount of coin on this quad. Where are you mostly going to ride it, Trails, MX Tracks, a mix of both, If it is a mix of both, how common is the lesser of the 2 places that you'll be in.
The reason I ask all this stuff if because the zuki already comes pretty well geared to the track, and with the quite core pulled out, and the cherry bomb ($45 part, yields close to 7 hp) which is a substantial power increase. But it's power delivery (from what I've read) can be a little touchy, and similiar to how a powerband of a 2-stroke can kick in, though not as drastic of a change. And on top of that with the added width, it may be hard to fit through some tight wooded trails.
Stock v Stock on a track I'd say the zuki should have the win with equal riders (not definate, but seems logical, and plus the cherry bomb is $45, and who can't spare that if you are buying the zuki.)
The YFZ (again from what I've read) is somewhat more trail friendly, ergonomically speaking. Though from quite a few message boards I've read on them say they are not as comfortable on them as they are on the honda's (but that is personal preference, and nothing a set of bars can't help out a little). But on the track and trails, I've heard that comparably mod'd, and stock v stock, the YFZ is generally more well sought after, power, and smoothness of power delivery wise.
Between the YFZ and the 450r, it's tough since they are both built as still in a basic form, and not as track specific as the zuki.
Take your time, go sit on them all. See how the quads fit your body, lean on then transfer your weight from side to side like your turning, see how they feel under you. Try to find out as much as you can about each of the 3 available so your not kicking yourself later...
Good Luck on your purchase, I hope that things work out for ya.
~Bill
