I can accept that Bucky and Steve are abnormally strong. I cannot, however, accept that they hit with a greater force than a fired tank shell. Because that's what Ironman took in the first movie, and it barely slowed him down. So atleast within the ballpark of that amount of force is what they have to be hitting him with.
Meh. I can roll with it. Stark has different suits for different moments so maybe this is just a weaker variant than say the Hulkbuster. Plus they can always just hand wave it away as it being the experimental bleeding edge suit or something.