Point of order, the katana was in fact very good at slicing through un- or lightly armoured flesh. This is what it was designed for, and what it excelled at.

As far as splitting bullets are concerned though, well I feel it is best summed up by the following clip.

[youtube]https://www.youtube.com/watch?v=1Qy-Be2cDGQ[/youtube]
Note the still very lethal high velocity shrapnel btw.