What if it it's a few times over the limit? Are engineers that
conservative on paper?
We don't know what the "limit" is though. We don't know how much energy Tony's reactor produces. I don't know enough engineering or physics to sit down and do an "energy budget" for all the armor's capabilities.
We're also talking about a world where, among other things, man can create a literally unbreakable metal, anti-gravity, unstable molecules, hand-held energy weapons, etc.
If you want to dismiss it as "handwavium", go ahead. All I'm pointing out is that within the context of the MU (even the movie universe), "super science" is a lot less "super" and a lot more "common" than ours.