There is also a number called minimum sink, which is commonly used by glider pilots. This is the speed that will allow you to stay in the air the longest. If you have a good landing site within easy gliding distance, you may want to consider using the minimum sink speed. It will maximize the time you have in the air to investigate the problem and attempt to fix it. Minimum sink is, however, generally not published for powered airplanes. You can figure yours out by going to a safe altitude and experimenting by pulling the power and noting the descent rate at different speeds. You will notice that, as you get closer to stall speed, the descent rate will increase rapidly for each knot you slow down.