I haven't entered into any competitions, but for what it's worth, the only thing that's limited me in mud is tire size (deep ruts) and fear of my 'Burb swallowing water/mud through the stock air intake location behind the grill. As long as my tires could reach the ground, the diesel has pulled me (and many others) into and out of mud with ease.
Jon /forums/images/graemlins/burb.gif