The maximum allowable torque must correspond to the allowable shear stress for maximization. To solve this, we use the torsion formula:
Max. Allowable Shear Stress = Maximum Torque ÷ Cross-Sectional Area
8 x 10^6 Pa = Maximum Torque ÷ pi*(d/2)²
Maximum Torque = 8 x 10^6 Pa * pi*(0.06/2)² m²
Maximum Torque = 22,619.47 J or
Maximum Torque = 22.62 kJ
As for the second question, I have no reference figure so I am unable to answer it. I hope I was still able to help you, though.
