Most engines are made to run 20%. If you want a quick boost, bump up. I suggest you add a thin shim under the head though to prevent breaking something.
Novice, 10% is fine, but if you want to compete, go up to 20%. I would run rich again if you do. The higher percentage, the more heat the engine produces. The more heat the engine produces, the more the internal parts expand. Allowing the parts to expand slowly by running rich and slowly leaning it out will extend the life of your mill.