The best oil pressure you are going to get with a drill motor will depend on the rated HP of the drill motor. A "Good" HV oil pump (for a BB MOPAR) will flow just under 20GPM/min,. To generate 40 psi with a 95% efficient pump you will need at least .5HP - 60psi will require .75HP. Now if the pump become less efficient (75%) you will need 1HP to generate 60psi.
All that being said looks like your in the ball park.( this is a simplified explanation without corrections for oil viscosity differences but gets the point across)