Setting that value to 10 might be wiser, 5 knife kills is not that much of an achievement, even I can easily do that. However, 10 is a different story on a full 32 slot TDM server. Most people get stuck somewhere between 5 and 10 when they are average players, so the flooding will stop if you change it to 10.
Furthermore when reaching 50 it should say something along the lines of "well done slicey, 50 slices!". Nobody but him can go up to 50 anyhow.