just came across this and i understand what yall mean about a reptile 40 not being able to hold water, etc....but I guess my questtion gos to the original statement of a 40b not being able to hold water...why would they make a 40B that couldnt?
With goldfish, wider is better. Most goldfish cannot withstand deep tanks anyway since the pressure causes them to lose their buoyancy balance because of compromise whether by fin shape or body shape. Most pearlscales have difficulty keeping their balance in deep tanks. Same can be said with tosakins.
In general, goldfish prefer longer tanks than taller tanks.
in my little experience long and wide is better than high and long for all goldfish except ryukins they seem to do well in deep tanks it may be because of there shape.
also if you ever get a chance to go to a chinese goldfish farm they seem to prefer growing the fishes out in long wide pools which are generally shallow.