I think it probaly will work, if you taken some precaution.
Based on the calculation, you have a bottom safety factor of 1.81.
Here's an excerpt from http://saltaquarium.about.com/od/diy...tomtank_3.htm:
Many DIYers have found that they can increase the Safety Factor for a given thickness and tank size by installing a 4" wide glass brace from front to back of the top of the glass, essentially turning their tank into two 2' tanks, increasing the Safety Factor to 3.38. Rather than go to a thicker glass to increase the Safety Factor, you can economize on construction in this manner.
So you have a center brace, based on the above, your tank is effectively a 2' tank. With that information, your bottom safety factor becomes 2.27. Still under the recommended 3.8, but....
You can also economize by designing your tank stand so that it fully supports the entire bottom of the tank by using a styrofoam or polystyrene pad between the tank and stand. The pad will keep the tank from failing due to a point load on the glass surface which can be caused by dirt or grit on the stand surface. If the tank bottom is fully supported, you can also use a thinner than normal piece of glass for the tank bottom, since the stand will be adding strength and support, keeping the glass from bending.
This basically mean that you need to follow the above advice and properly support your tank. Now nothing is 100%, if you want added safety, I recommend having at least 3.8 safety factor for the bottom also, which mean going to the next thickness grade, 9mm.