Fast/Slow indicator gives indications relative to 1.3Vs and is applicable at all times during configuration changes. ie. if flying with the indicator in the middle (1.3Vs) you have the same margin over the stall whether you are clean or have full flap.
Putting all that aside in case I am just going up the wrong path, what profile would people fly following failure of all engines? Talking large aircraft here, not a little piston that probably just has a standard glide speed.
Anyone?