Simply put it is mostly up to your personal tastes as a Tattoo Artist but the general rule of thumb is the thicker the spring the faster it will go, so for example you may use .013 - .018 for a shader and .017- .022 for a liner, you may also change the gauges between the main (back) and timing (front spring) but generally only within .002 eg. .018 main .020 timing. its all personal preference. I do know that if you try some better stock springs and still have problems, there is o harm in trying 18g springs. I have a high hand speed and have always liked 18g springs and the jump in voltage is not surmountable enough that it should prove problematic. just my two cents. but you have gotten some good advice from these other guys, so I hope it works out for you :-)