We did some lake bathymetric mapping in grad school. Unless there are specific meaningful breakpoints in the data, I would avoid using anything other than the standard (equal interval) classification behind most bath maps; 0-5, 6-10, 11-15, etc., especially on public maps, the deviation from a "typical" classification will only confuse folks. Although I would make sure to include the limnetic/profundal breakpoint (or zone) in the classification (i.e. 0-5, 6, 7-10, 11-15) with explanation in the legend.
My two cents.
-Bob