Just been for a blast on some new, very clay'y trails and my Maxiss Advantages (2.25") which I've grown to love on sandstone type mud were rubbish. They became 2.5" slicks within a minute or two and, well, my knees, shins, elbows and balls all hurt after several almost-amusing offs.
What tires for very clingy mud?
edit: Oh, going on a carbon HT. I couldn't go much bigger at all than the Advantages already on there.