musta-
My "very stable" term is relative, not quantifiable. It was used mainly in response to erikv's statement about speeds above min drag to be "stable". Reading his post (first paragraph) might leave the impression that MRC is in the neighborhood of min drag. It's not.
Any speed above min drag may be "stable" in the technical sense, but in real life, at speeds around min drag, you will be paying a lot of attention to throttle position.
For example on my DC-8, at 300,000 lbs, the LRC is M.81. MRC is M.79, hardly enough difference to call it an "unstable speed". At Min Drag of M.69, it will be unstable, meaning it will require close attention.