Interesting question. In my 110g cube, those 11 fish work out to about 42". Haha, I have a way higher ratio than you do in your 400.
I have an eel though which sort of skews the numbers. Well, actually, I guess it doesn't skew since he puts a pretty heavy load on the tank, at 8" he's probably way "heavier" than the 8" tang, for example.