Well Iron Man did OKish against Thor. If you take the crossover comics as canon, Thor = Superman Although Thor would later say that he knows Superman's limits and that a rematch might see himself as the victor. Playing in to the fact that Thor is very arrogant and doesn't give his 100% against every opponent he fights. And yes not even Superman can lift Mjlonir with pure strength alone. Just like the Hulk could not in the Avengers. Iron Man's has a chance if he disable one of the Krytptonian breathers or deliver an awesome repulsor blast that incapacitates a Kryptonian.