I would suggest a DV8 Marauder Madness for a medium oil ball. The box finish is at 4000 to get through the heavy head oil, but it can be polished to give a more angular reaction or it is starting up too early. This ball is great for house shots or sport patterns, and would be a great benchmark ball.
Another ball that would work great on medium oil is the Brunswick C*(System) versa-max. This ball is very versatile! With its higher RG value, it will clear the heads, store energy, and finish with an arcing motion. It can be kept in the box finish with the polish, or can be taken to 2000 or 4000 to smooth out the reaction.