40:1 is a pretty good average, although it varies some with the sugar content of the sap.....which also varies according to time of year, and the variety of maple you have tapped. 2.5-3% sugar content is considered great, and some producers will check this with a refractometer. The higher the sugar content, the less time spent boiling.
I just tap the trees and boil...I have plenty of firewood for fuel!