I have seen pentagons in many sizes as well as the corner bowfront tanks. I do not know about the smaller bowfronts and the distortion there, but the larger ones have such a gentle curve that the distortion is non-existant. I have a 60 gallon corner bowfront as well as a 55 or so pentagon corner tank. I like the bowfront ever so much more - it is easier to clean and the fish do not get distorted in the corners - for there are none.
The hexes that get larger than the 44 seem to be made taller and not much wider. The 60-ish that I have seen has the same footprint as the 44. So much less surface area to a tank shape that already has some problems - not so good, I would think.
An octagon would be nightmare to clean - all those corners to collect algae! And it, also, would probably have surface area limitations.
A triangle tank - that sounds cool, but would probably lend itself to distortion difficulties, too.
There are custom tank designers in almost every city - there is a fellow here that will make a tank for me in any shape and size I want - and his work is competitively priced for any "AllGlass" tank of similar square footage of glass. You might try to find someone like that and ask for the tank you want.....
You have some unique ideas - I bet your tanks are really individually exciting to see!