Gear Strength & Shaft hole relation

Would you please point me to a reliable source of reference that will tell me what relation exists between the Stregnth of a Gear material and a hole machined into the gear.

Say I design a spur gear pair, selecting its module m = 7 & number of teeth Tp = 20, thereby finding its mean diameter, and evaluate that a gear of such dimension, in order to sustain the load, will have to be machined out of a material having a UTS of 750 MPa.

Now if I were to machine a hole of 50 mm through the gear, then by what amount would the required UTS of the material be increased so that the gear can sustain the Torque and load it is expected to take and would have taken had a soild gear been machined with a material of 750 MPa UTS

A reliable online publicaly accessible source of reference would be highly appreciated

TIA