I have owned both machines, and in my opion I think they both perform well on tight trails. Infact I can't say that either one is better than the other. However, if you are talking power, then the z will eat the ex for breakfast, and my z will lug just as much as ex did. My z actualy has more bottom and top end than my ex. The only regrets that I have on the ex is that mine didn't have reverse and that I am not too crazy about how the old ones look.

 

Arts snowmobile and ATV has a sale on big bore kits for 400ex...440ex big bore kit with 11:1 piston and cylinder sleeved and fitted..for $359.00...its a hell of a deal bolt on ready..get after it