Andrew, on Monday I hiked about 17 miles with the Delerions with a full backpack (About 20 lbs, desert hiking, refilled water with purifier but carrying about 1 gal at start because of dry conditions). About 12 miles of this hike was off trail. The remaining five on abandoned jeep roads and a short section of trail.
The TechAmphibian Pros have a mesh that let in lots of dirt. Even my North Face Ultra 102s under similar conditions, my feet would have looked pretty dirty after so much hiking without a trail. With the Delerions and the gaiters that come with them my feet were much cleaner! My feet also keep much drier than with other shoes, like the North Face Ultra.
There is a mesh on the Delerion but the "holes" are so fine that I didn't pick up any cheat grass in these panels. I was shocked. It normally clings to and penetrates the various lightweight shoes I use with ease.
Tomorrow I'll be going on an 11 mile hike in the desert near here. I will collect dirt, sand, and the bentonite clay that is common in the desert in this area. I will then experiment with trying to push these substances through the Delerion wall, using dry and wet soil. It probably won't be the same as the test you would like, but it should be informative.
Another comment: After returning from the 17 mile hike I normally take my trail running shoes off in the bathtub, dump out the sand and dirt, and knock the shoes against the side of the bathtub to "clean" them. The Delerion's left almost nothing in the bathtub. The North Face Ultras practically creates a sand/dust pile in my bathtub.
There is no doubt that at least for me, the Timberland Delerion, is now my favorite shoe for the broadest variety of trail conditions.
I'll report back on the mud, dirt, sand, test on the shoe wall within a week if at all possible.