start at around 7v and work you way up.
Also if you want it whisper quiet with a much smoother action like the bishops,neos,impacts you can take off the slide and drill a small hole in the center bottom of it and and a small dimple in the frame channel-a small spring will go in there between the two.
You can get them from bishop etc. A harder spring has less needle time in the skin and faster return for lining and a softer one for shade/color which keeps the needles in the skin more with helps with healing and saturation.