I have gone back and forth on tires for the last couple months.
I have decided to just stick the cooper discoverer st tires pictured above on my dually.
I want some mud tread but I want some street handling.
Cooper also makes a discoverer sst in the stock tire size and this is an even more aggressive mud tire in an E load rating. I figured I would lose too much street handling though.
With something like a 2 inch spacer you will need longer studs and you are moving the tire 2 inches further out. And keep in mind the bigger tires often are wider than stock so you can sometimes wind up with 2. 5 or 3 inches or more tire moving towards the outside of the dually fender. I have never measured what that would do since the stock rims are so narrow I won't go wider since I don't like how wide tires handle on a narrow rim.
Anyway, I highly recomend some searches on spacers and stuff since that gets discussed in all forums now and then and there is a lot to consider in my opinion.
And I don't know tire sizes that well but the one post about what fits up front vs. what fits in the back could get into problems when using 4x4. You should keep tires sizes the same height so the gearing does not get into binding. I could not tell from the post what the thinking was, so don't get offended if you already know this. I figure better safe than sorry.