Ulrich, there's a difference between 'smacking' with a katana, and using proper technique. With a decent sword and proper technique- you can do a lot of damage to a person, whether or not they are armored. NOT a good idea for you to move ahead with such a 'test'- I'm sure I speak for the rest of us when I say we would strongly advise against it.
Especially with the questionable nature of some of the maille armor that's available these days- who is to say it is more protective than what was available in antiquity? In short, it isn't worth getting injured and possibly maimed yourself to find out.
FWIW, the curve of the katana lends itself very well to cutting, better than a straight dual edged sword imho- nevermind that I prefer the Euro style sword first and foremost. Also, contrary to popular belief, katana are quite well suited to the thrust- the thick spine and short but wicked point are nothing to be considered lightly if facing an opponent wielding one.