32" or 33" MT tire on your current rims. The MT will be good in the soup, and most of your use. 6-8 trips on pavement, def. will be secondary consideration. So go for the MT's or an aggressive AT w/ open lugs for your muddy conditions.
stay w/ current 15" rims.
=cheaper
= 7" might be skinny but w/ 33" aired down, you will have a good footprint. Skinner might even be an advantage in certain situations 'cutting thru' muck trails...
16" rims
=allows a wider tire
= looks better
=more plys = more protection from flats
you loose a lot w/ 35s and no regear so I would keep it 33 max. In the muck, you might need every bit of hp to get that heavy diesel thru!
33's look great w/ the OME lift and you don't sacrifice too much power.
I can't remember the choice tires in AUS but I think they were Pro-Comp MT, GY MTR, Toyo MT (and the BFG MT were not as good.)