Process design conditons are (steam) approx. 20 psig and 275 degF.
Valve supplier quoted a class 150# valve with a very larger motor operator; stating that to meet the closure test in B16.34 the valve operator needs to be large because B16.34 requires 110% of the 150# Automatic Control Valves rating or approx. 110% of 285 psig.  it seems to me that the operator should be sized to operate the valve against the maximum design condition, in this case 30 psig, and not the 110% requirement of closure test, which once installed the valve will never see those conditions but will have an operator sitting there just waiting for it to happen.
Actuators must be sized according to maximum expected operational torque over time. This increased torque will be depending on valvetype, design, adjustment and application, and also normally be the torque loosening valve from seat after long periodes in closed position, with or without fluid or load.
Over time this torque could easily be increased from initial required torque to considerably more, x 2 or more under unfortunate conditions and poorly managed plant.
Purely guess from my side: seems that you should discuss point 2. with the supplier, but that considerations on extra torque could be reasonable, but 110% of what? Load or what torque? And why large actuator instead of smaller plus gear? Details needed from supplier!  

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