Ive loved the Donelly PDX, but havent tried the mxp. I feel like the wider spacing of the lugs, as compared with the mxp, allow the lugs to better dig into grass. Where we ride, in the south, the big challenge for the tires is to hold a curve without washing out on wet grass/mud. Another note, I also liked the shape of Donelly tires compared with the Scwalbe’s I had a few years ago. The Donelly’s were rounder and I could more easily roll the bike over to grab with the side knobs rather than just turning the bars. YMMV.
That being said, Ive got a set of the maxxis All Tarrane’s that came on a recent purchase, and Im going to give those a try this fall.
Also, get one of those digital tire guages and really dial in the lowest pressure you can without ripping the tire off the tubeless rim.