Superman looses, if gladiator is fighting to save the shiar, for the honor of the shiar(superman insults them), or if gladiator is really pissed off.
He would be at full confidence and that is like pre-crisis superman level.
Glaidiator ripped stars in half, fly at 100 x light, and etc.
At that level, he'd only have to hit post-crisis(assuming that is who he is fighting) superman 1 or 2 times and his lights would be out, for good.
If gladiator isn't at his full capacity, he might have a problem on his hands.
As for, the confidence thing, its true(mostly), but then again, the same can be said for superman.
People are so quick to bring up the "confidence" thing with gladiator, but they don't realize that superman is the same way, he rushes into some battles thinking he can just walk up to you and punch you, then he finds out the person ain't so easy, then he gets his ass kicked.
Yeah, they may write it so he comes back and wins later on, but the true remains that he initially gets his ass kicked.
So this fight could go either way, if not for the fact that a confident gladiatort is still leagues above a confident superman.
Not to mention gladiator's superior fighting skills.
Superman looses, either way.
(p.s. don't say gladiator is a superman rip off, cause he isn't.They have some simular powers, but they also have some diffenrent powers.
If thats the case, then every hero is just a rip off of the previous one who had a few simular powers.
And still if it were true, it wouldn't change the fact that gladiator would kick superman's ass.)
Samuel Jackson, beer-maker:"mmm-mmmm...Good day to you, motha****a!"