Iv run the 130 S12XC and the 120 MX31, both work very well in the sand, I could climb decent sand hills from the bottom with little run up with the mx31. Both worked well on slippery clay and in muddy trash. I did find that the mx31 if run for too many hours would tear off side knobs, maybe ~20 hours. M400 series are also very good tyres imo, the rear seems to round off centre knobs fairly quickly, but the side knobs are sharp for a long time. Im currently running an S12XC rear and an M403 front, works superbly. All sets of name brand tyres cost the same for me so I use the ones that work the best, as is stands I really like the s12xc/m403 combo.
