A/F gauges are a tool, not a very good one, but a tool nonetheless. Our engines are very sensitive to knock, or rather, our pistons are very sensitive to knock. If you can hear knock it may be too late. I got lucky this past weekend, I've had some minor knock issues (barely audible) but it was very warm this weekend and I got KNOCK, very loud, very scary. My timing was keeping EGTs in check but I was just running too lean for the temp conditions. Problem solved and, thankfully, no damage.