I just bought a Fyrite Tech 50 and am using it on an older Burnam oil fired boiler which has a newish Beckett burner installed. I get visible smoke unless I have about 18% or more excess air which yields about 84% efficiency. I can get up to about 85.5% efficiency with about a #3 smoke.
My understanding is one can tune for higher flame efficiency which results in more smoke which will soot up the boiler decreasing heat transfer efficiency which greatly reduces overall efficiency. It sounds like going for zero smoke is the way to go.
Do my numbers and thinking sound about right?