Superman can withstand over 50 supernovas going off at once and survive.
Superman has lifted over 200 Quintilian tons (Regular superman can do 6.6 Quintilian)
Superman can hold black holes
Superman can fly 18x the speed of light
Superman is immortal (If he stays within yellow or blue sun energy distance)
Superman durability is at 10 octillion
Superman is basically un-killable (Unless he is presented kyrptonite, magic, red sun light)
Superman's brain can process things 10,000x faster than the human brain.
Thor max lifting capabilities is 2 million tons (With the belt it's doubled.)
Thor can survive a black hole since he can go 2x the speed of light.
Thor's durability is not on par or even close to Superman's.
Thor can fly 2x the speed of light (As I previously stated)
Thor has no known weakness other than his urge to fight when a fight a presented to him.
Thor is immortal (Unless he is killed of course)
He can manipulate magic, which is one of supermans weakneses (but nothing superman cant out think.)
So rationally speaking, who do you think would win this fight?
Side note: If superman is fully powered he can withstand Thor's magic to a certain extent.