I have tried to make 120 gallons (48inx24inx24in) (0.25inch glass thickness) and worked fine..at 1st it made my bottom cracked due to unleveled ground,so i replaced the bottom and made a sturdier stand and cemented the unleveled ground,now its been a year.
Flex can be taken care of with braces. The reason acrylic can be thinner is that it can hold more pressure per square inch. (Pressure from the weight of the water pushing outwards.)
good but there missing the surface area of the glass factor... like a 4x8ft will break easier than a 1x1ft even if there the same thickness and tank size... so you also meed to figure that in not just how high and also where the glass is place if you have a tank and the window is higher than the bottom than theres less pressure
I do Know for sure that glass thickness has nothing to do with depth(front to back) it has to do with how tall the tank is. So the difference of just a few inches can be fatal if the thickness is not exact with the height.