Cove Stiffee: I have a pair of super tacky Swamp Things on. It grips and I like it.
GT Avalanche: Currently have a pair of Continental Verticals. The front always feels fine, but the back end has poor grip over roots and rocks (it's a bit of a shocker).
I have a Super Tacky High Roller which I am inclined to put on the front of the Cove and put the freed up Swamp Thing onto the back of the GT. Also, the High Roller is directional (only indicates one direction) but from looking at other tyres it looks wrong for the rear.