I'm looking to go the other way. I'm getting to a point where my speed on the straights on rocky trails is fast enough to trash my 17" rims. I need more sidewall for the square rocks. Also some knobs would give me a faster corner speed I think.
Have 3.5 and 5.0 x 17" rims and air down to 15 to 18 psi for trail work. It works very well for what it is. Phenom braking and little wheelspin on loose climbs. The 160 rear has a massive footprint at 15 psi. Can climb slow or fast without hardly any kickout.
To keep my forks and radial caliper I'm thinking of getting a 19 x 3.5 complete front wheel and a 4.25 x 17" rear rim. I've already got spokes and a Kush hub. The 4.25 would give me many d/s tire options. A 21" wheel has caliper/spoke interference problems.
Or I could just get a tire changer and go with a taller front 17" for trails. Mark where the weights and valve stem are so balancing is a non issue.
Not going up these at speeds. Just tractor up slowly and pick a good line. The street tire hooks up well and can loft the front up easily.