No first hand experience w/ the 38" nittos. I run little 35" big horns haha.
I know one guy from Idaho that runs the 40" mud grapplers (load range D) on a cj7 and he does very well. They are grooved considerably but he uses them for snow only and runs them at very low pressures.
Next snow season I will have a set of the 38" nittos on 15x12 allied beadlocks. I am planning to only groove them, no siping. My CJ is 3000lbs ready to rock. Should float awesome with the big balloons.
Any tire will dig if it's not broken in and/or has too much air in it. I constantly run my tires 0-2lbs when snow wheeling. I found my jeep goes best when there's just enough air in the tires to keep the inner bead from falling off
I like to snow wheel