You can't ride them both and judge for yourself? 2cm isn't a lot, but when I bought my Atlantis and followed Rivendell's sizing recommendations, I wound up on a bike 2cm bigger than my previous ones, and it made a lot of difference (to be fair, there were other factors involved, including higher handlebars and a Brooks saddle). You can compensate for a short top tube with a longer stem (it's not ideal, but it's commonly done and it works).
How did you determine that the tubes were too short, and by such precise amounts? Rigid rules about fit don't always apply to all riders--they're often based on what the pros ride, and many of us aren't comfortable with that setup. I'd really try to ride them both for at least 15 minutes or so apiece, and don't restrict your test to the top tube length. Evaluate the components, the condition of the driveline etc.