Both will be fighting to their full potential, meaning Thor would fight with the full power of his Power-Gem and possess infinite strength and stamina with the Power Gem and Superman would potentially be fighting with the strength just as unlimited. Flying is prohibited, they are only allowed to fight on in a cage; so who'd win??
I personally believe Thor would win this one as that Power Gem obtains him all the energy in the entire universe to amplify his strength and stamina which would mean that Silver-Age Superman's energy would also be absorbed to Thor's body as well as being combined with every other energy system Thor acquires. Superman also has vulnerability to magic, Thor possesses attacks that could obliterate planets at full potential and also contain magic including the God-blast. PC Superman is more vulnerable to magic than Modern Superman so I believe godblast would be enough to shatter his body.
Thor had the ability to destroy an entire galaxy if he projected the explosion he could have formed after absorbing energy from the "Null Bomb" (A weapon created to devastate galaxies) and he could have destroyed more than just 1 galaxy if he amplified the energy contained in his hammer. Imagine what he could do to the universe and SA Superman with all the energy in an entire universe.