Hi, reply to old post but did you get results from this experiment?
So far my findings have been that it depends on genetics. Smaller/faster autos don't see much benefit going above 10l, but some will do much better in 14l containers. Pot/container shape (within reason) does not seem to matter as much as total volume. I now have a good mix of 10 and 14/15 liter containers which I use depending on strain.