You guys gotta realize that different engine respond differently to timing changes. Between, porting, static compression, altitude, fuel type, and ambient temps you can jump the timing up a good bit, or even have to retard it for max performance. Theres really no one number for them all. Plus the smaller cc higher revving engines will typically see better gains from more advanced timing. Just have to keep it conservative enough to allow easy starting. That's one of the biggest down sides to fixed timing. Your trying to get best overall performance. Not ideal for top end but good enough to start the engine and get good performance at the same time. I'd wager a small amount that most of our engines could take a few more degrees advance and be non the worse for it.