bsmet95,
The allowable surface pressure (also called contact stress) will be a multiple of the yield stress, not a fraction of it. As an example, Hertzian contact stresses for gears and bearings may be > 2000 MPa and still be considered within the allowable design requirements for high cycle loading (see ANSI/AGMA 2001-C95, ISO 6336-1, etc.). Perform a keyword search for contact stress or look through some machine design textbooks.