No, I'm not going to be stupid & say that on any given day Iron Man can whoop on Supes. Thas dumb. But I will say that the fight willnot be an overwhelming asswhoop like Aunt May vs. Juggernaut.
1) Strength: IM is outclassed. Superman is way over what his suit can do, but, so is the Hulk and IM has taken on & beaten the Hulk before.
2) Speed: Again IM is beat. If Superman pushes it, there's no way that IM can keep up.
3) Fighting Style/Method: Supes will have no problem coming right up in your face & smacking you around. Seems he'd rather do that than shoot you from a distance w/ heat vision. His arsenal's kinda limited to a few tried & true attacks, but he's no one-trick-pony.
IM on the other hand would gladly pick you off with around 50 different types of distance attacks (repulsors, missiles, buncha shit...) and think out your weakness before going in too close. Plus with oogles of technology at his aide, he could build another suit that would fit the fight better.
Now, I know Supes snaps sometimes & goes nuts & all, but as stated before, that usually happens when a teammate dies or something drastic & this is one-on-one w/ no teammates involved. Now, although the issues weren't all that great, do you remember when IM went bad? The guy took on an entire Avengers team (albeit weakened version) on his own, no small feat.
I still think my boy's end is near in this one. He could take the Hulk b/c the Hulk was just strong, not smart, and kept his feet on the ground. Superman excels in too many levels: strength, speed, intelligence, flying ability (not fighting ability). Would take the ultimate trump card, Kryptonite, to put an end to him.