Don't get dragged down the size route, off road its irrelivant. Nothing to go with contact area. A lot more to do with the block pattern and spacings. Will it self clean, have you the horsepower to spin it up. Just fit tyres the right size.
And the biggest issue mud. It will stop you rapidly if you have minimum clearance for the tyre, i used some on my DT that still left me with a good inch of clearance and got stuck on a climb because the mud jammed up the rear wheel. Your system is better as you haven't the sidebraces to help trap the 'mud'(animals use them trails too).
I rode the ridgeway on std bridgestone trailwings more than once, in the company of full MX shod enduro bikes. They were all amazed at where the little DT would go, in the end i just had a knobbly on the front and stayed with the bridgestone on the rear, (losing the fron hurts more) after trying a couple of different options, i found being able to spin the bo77ocks out of the rear far more usefull esp on climbs. Nice big fantail of mud and sh1te