i actually own both a shee and a z400....they both have their ups and downs..
the shee has the wheel-lifting hard-pulling ass-puckering speed....absolutely AWSOME on a most wider trails.
the z400 IS alot easier on the real tight technical trails though....and it is better on fuel.
the shee will run down the z400 in a heartbeat...
i love em both but the shee is more of a blast to ride...but if you ride LONG LONG distances your gonna need to carry oil or you wind up buying oil for a rediculous price and its usually not the same stuff you normally run...i actually built my own oil carrier that mounts inside the frame and carries enough to fill a full tank or measures out enough to fill by the gallon.
all in all they are both good machines.....the shee will need a rebuild earlier as its a 2-stroke.....but they are WICKED easy to rebuild as apposed to the 4-strokers