From Captain America: Winter Soldier, during the scene where Steve managed to pin Tony against the war and punch him left and right, we can see Tony's HUD when it's analyzing Steve's attacks, it seems that Captain America is delivering blows in a range of about a few hundreds to a few thousands N.
This implies that:
1. Steve is holding back (unlikely).
2. Steve punch less hard than an average, trained boxer.
3. Tony's suit can be damaged by only half the force of an average, trained boxer.
I have a hard time believing my implications are true, so I come up with an explanation - The "decimal" in the HUD is actually a comma (it's a bit too small to distinguish properly), which means that Steve can punch upward to the range of 200,000+ N, this is about 59 times more powerful than what an average, trained boxer could dish out (~3407 N converted from 766 Pound-force). Not unbelievable considering that Steve can stagger Thanos with his punches.
Of course, this isn't a definite proof to MCU Steve's striking strength, but the small details the artists/editors put into makes it interesting to analyze.
What do you think?