It also depends on the weight of the aircraft you are trying to descend efficiently.
A "H" aircraft near or at MLW will need a max of 3 deg decent path. If it is empty with minimum fuel you could be looking at more.
A "M" aircraft, 3 degs power off will not really be 3 degs. 3.5 or more if you are light with wind considerations.
Just my 2 cents worth having operated heavy, medium and light aircraft.
Weight plays a very big part in this. Ask your selves why a glider takes on ballist to increase speed for a given range.