Like efficiency, I think this is a spot where it is easy to get stuck chasing the dragon. Do what works for you and makes you good beer. I am confident that I have as little boil off as possible in my current environment with my current kettle and burner. I'm happy, beer is good, I'm moving on.
Percentages of boil off are absolutely useless here, IMO. Geometry, temperature, wind, and humidity all play a role. Plus when I brew 5 gallons, the boil off is the same as when I brew 10 gallons.