Glenn, since you build custom tanks and hoods I'll defer to your knowledge but I've always understood that glass thickness is more dependent on height than length or width. Properly braced shouldn't a 2 foot high tank be more than safe using 1/2"? I'm really interested because my tank is 30" high x 6' x 2' and a wood/glass hybrid. The glass store that I'm ordering my "portal" from insisted that 1/2" would be fine, that they build tanks that high all the time with 1/2". Mind you, they sell 3/4" which is what I first asked them about and they said I'd be more than safe with 1/2", not to mention the 125 or so extra pounds of the 3/4". Thanks for your input.
Later, Paul