With the right offset you can likely get 275's on the rear but IMHO 265's look better and that is what I run. It is recommended that you have a 9 inch rear rim for anything over 255. 265's and 275's will run on a 9" rim. On the front anything over 235's will likely rub under aggressive driving. This doe not apply to the "M" model. Keep in mind that the stock dia for the standard Zed is for a 25 inch dia tire.
If you go to the WEB site for the tires you are going to use you should be able to get recommended rim sizes and diameters for various sizes of tires.