Most of the Italian motors are designed for 25% because that's what they get in europe. I like the Byrons 25%. Plenty of power & no re-shimming the head. Most manufacturers advise adding a shim for use with 30%. I have not run the NEW Byrons yet but if there is no 25%, I will shim all my motors & run the 30%. You can feel the the difference between 20 & 30% if you run them back to back but if you cannot win with 20%, 30% will not make the difference.