For a 38.1 x 2.413 mm (1.5 x 0.095 inch) round tube, versus a 38.1 x 2.413 mm square tube, the moment of inertia of the square tube is 1.70 times the moment of inertia of the round tube. Therefore, in an orthogonal direction, the square tube elastic bending strength is 1.70 times the elastic bending strength of the above round tube. In the 45 deg direction, the square tube elastic bending strength is 1.20 times the elastic bending strength of the above round tube. I have not investigated plastic bending strength yet.