What current and voltage are best for electrolysis rust removal?
In order to answer the question we also need how large a part you are electrolyzing. 

The current density in $mA/cm^2$  is the key number. For electrolysis on stainless steel, I would say you need to stay less than about $ 1~mA/cm^2$ to stay safe. 

The voltage is hard to gauge. In any two electrode system like yours, the electrochemical potential is only one part of the total potential. The total potential includes contributions from the resistance of the solution, resistance of the contacts, overpotential of the counter reaction, etc... The current should be a decent gauge of what you are seeing.