what size offset will I nedd to clear, 27-10-12 on the front and 27-12-12 on the back

 

That partly depends on what brand of tires and wheels you are going with as the tires do differ in actual measurement. I have ITP's on my 800 with 26x9 up front, they have plenty of clearance. It appears that another inch of width would still allow plenty of clearance. I know the height is not a problem as I have had my wife's on it. Depending what you do with it, though, you may want to consider a 2" lift. I don't think they will rub though. Why would you want to go so wide up front? Keep in mind this makes steering more difficult....

BTW, there are some recent posts that explain all of this and the offset...

Enjoy the 27's! They look good and work even better!