I'm not Airbus rated, but it's my assumption that the Green Dot equates to Best Angle of Climb / Minimum Manoeuvre Speed / Best Holding Speed / Engine Inoperative Drift-Down Speed, all of which are fairly much the same with only minor differences to Vmd. If my assumption is incorrect, please do not read further.
Be assured that Flight Planning will be based upon Cost Index (CI), which nowadays lies somewhere between Max Range Cruise and Long Range Cruise.
Cruise at your best Holding speed (if my Green Dot assumption is correct) would be disastrous from a Flight Planning point of view. VERY high altitude cruise COULD result in Green Dot being close to CI speed, this would be the exception.
I'll delete this post if my Green Dot assumptions are incorrect, promise.
Regards,
Old Smokey