The form Cap fought was not more powerful than the one Iron Man fought. We have no evidence of that, and common sense doesn't even help its case too.
Also, Iron Man was having trouble with Ultron who was throwing debris, shooting lasers, flying around and away to delay him, but ultimately fell to a single missile. Whereas Cap only ever dealt with him physically and his lasers. Ultron also flew low, and tried to bullrush a guy whose forte is close combat.
Make no mistake though, Cap's showing there was impressive. If anything, he should be in the small building range, imo, but that's just me. Though, let's not bring too much comic stuff into the MCU because not everything applies, like for example, nobody in the MCU reacted to lightning, and the only lightning feat we ever saw onscreen was Dr. Strange and the Ancient One speaking in a time-slowed dimension and we see a lightning bolt sluggishly moving in the background.
Re: Thor, Cap did not intercept Thor. He blocked a telegraphed jump and smash obviously aimed at him, had the advantage of standing his ground, shield up, making it near impossible to fling him away, as compared to say, him catching a grenade launcher from the side. It's more a shield feat than a strength feat for Cap since it deflected all damage outward and away from him, making contact with Mjolnir too little to actually flatten him (constant pushing will throw Cap backwards but very brief contact very likely won't) since it pushed Thor away with his own force.
Also, how is subsonic Thor funny? Only feat we have of him being above subsonic is the dubious Mjolnir has an MHS feat, unless you know of something else that we don't. I'm not even against Thor being higher than subsonic, since AoU showed that him moving his arm is faster than Iron Man and Cap's body, only eclipsed in that Pietro-vision in speed by repulsor rays.
He's subsonic+ now too, scaling from Hulk who scales from Abomination.