12.5-13.0 for best power. Stock is already 12.0. The tune will be safe at 13 as long as you keep the timing in check so you don't detonate.
13.0:1 is always the best a/f ratio for power. Even on my car that makes 700rwhp at 23lbs of boost is tuned to run 13.0 at WOT but I spray meth on top of that the keep it safe.