I suppose an important question is whether you need grip primarily on mud or on wet rock? The latter is mostly about the tyre compound, while mud performance is mostly about sheer knobbliness.
I find that that hard-packed ballast type surface as in the photo benefits from a wide (by road standards) tyre for comfort, and that general skittishness can be greatly reduced by careful choice of tyre pressure. Something like a Big Apple would work reasonably well there, while still rolling well, but wouldn't be the best when things get slippery, and it doesn't sound like you've got the clearance for a 50mm tyre anyway.