Min speed clarification.
The reason I don't fly below drift down speed is, 1. It gives adequate margin over the stall, and 2. Drift down speed is your initial target speed or min speed if you like should an engine failure occur. If you fly below drift down speed, and you do lose an engine you will have to descend immediately, and part of the procedure regarding RVSM is to minimise your altitude loss until 10 nm off track. Remember you will be turning as well. Do you want to be doing this at low speed?
The point is not so much what speed you chose as your minimum, but being able to justify why you chose that speed.
Back to the 767, Min speed at sea level is Ref30+80.
At 37000' +17 kts, min speed is Ref30+97, which is within a couple of knots of the book figures for drift down speed. There is method to their madness.
At no time does the book figures or the FMS give a Mach number.