27 or 28in megas!!??!

I just bought a 2011 grizz 700 that's pretty much stock. I'm looking to get bigger tires and think I've decided on mega mayhems. But can't decide on the size!! Thinking about 27in or 28in with a clutch mod? What size do y'all think is best with no lift and should I do the same size on all four corners?? I ride a lot of mud, damn near all I ride. I kinda like the idea of 28 in. Mega mayhems And a clutch mod. But what type & brand of clutch should I go with and what size tire on front & rear do y'all think??