As a general rule, the best glide angle in auto is done at a speed about mid point between the best rate of climb and the best range speed. If you have a headwind, add about 1/2 to 2/3 of the wind speed to the glide speed.
Why is best glide related to best range? Because both measure the least energy used per mile of distance traveled, since fuel burn is the same as altitude lost. Why is autorotation best glide speed slower than best range? Because the freely turning rotor trims to a lower, and worse rpm at the higher speed, so we take a bit of airspeed off.
For least rate of descent in auto fly at best climb speed, because that is the speed for the least fuel burned per minute to stay up, or the least altitude lost per minute.
Example: If the best range speed is 125 knots, and best climb speed is 75 knots, best autorotative glide is probably 110 or so, and min rate of descent in auto is about 75. If there is a 20 knot headwind, best glide is probably about 120 knots.