Wow, there are a lot of misconceptions about glass thickness and pressure being thrown around in this thread. Let's see if I can help clear things up.
Length and depth both have to be considered when building an aquarium. The wider the tank, the more directed pressure on the front viewing pane. The very center of that pane will receive the greatest stress. Bracing does help with this in that it reduces the pressure in essence by dividing the tank in half or 3rds or whatever depending on the number of braces. The pressure on the ends does not increase by any significant amount due to length, the outward pressure is static on all panes, volume does not affect this, depth does.
Your design is 135 gallons, it has a safety factor of 1.6 without bracing. With bracing similar to what you are calling for it should have a 3+ safety factor.
As for the reason everyone is saying that the tank is small for your fish is that they don't have a wide enough area to comfortably turn around in. Widening your tank will not reduce your safety factor. You could easilly build it 120*20*20 with the bracing you plan to implement. A word of caution however, bracing does not support the entire pane, only the top. This means that although it does help with structural integrity, it cannot overcome the pressures of depth. Be wary of that when you build.
I'm not sure where you are getting strange numbers from when it comes to calculators, though if you used some of the broken ones like the calcs based off of the New Zealand calculator you could get false readings on a few things... I'm pretty sure that the calcs on the sticky all use basically the same formula, and it is correct.
