Superman is still only a 'terrestrial'(I use the word loosely) hero though. Thor is brought in to fight the likes of Thanos, The Celestials, and other cosmic entities. His power is so incredible that there is not set way to describe his powers. He also uses one of Supes' two weaknesses...magic,and he's also been fighting for thousands of years so his combat prowess isn't even matched by the likes of Captain America or Wolverine. Is he as fast as superman in a fight? This is truly the only advantage Superman has over Thor, but when you have a area of effect attack that can drop a Celestial then I'm thinking you could drop Supes as well. Superman is very powerful yes, but Thor is unbeatable when he takes an opponent seriously and doesn't have some dimensional shift disease(Like when he fought Juggernaught.) Speaking of the fight with Juggernaught can Supes breathe in space(It's been awhile since I've read Superman comics and I don't know what his current power level is.)? If not then the same strat would work...transport Supes into deep space and game over.