Although Iron Man and Captain America are allies they came to blows twice during the Marvel Civil War. back in 2006. It was a good story.. In the first battle Iron Man nearly killed Cap. In the second, Cap gave up when he realized that innocent people were being caught up into fight between the two fractions. But what would happen if they both went all out? I think Captain America could win. I mean it won't be pretty, but i think he would find a way. Here is a fight in MUGEN.