Simple question, complex answers. It depends on the sophistication of your Flight Planning System, the airline operator parameters and restrictions used, and the operators planning priorities for fuel and time.
The most efficient is to use Cost Index, based on a City Pair generated cost index.
The speed on the CFP will be a function of the CI, weight, environmental conditions, airspace restrictions (fixed mach areas) and minimum/maximum speed schedules.
With the use of CI the speed can vary from MRC to just below VMO/MMO, far above LRC, which in simple terms is 1% SFC reduction from MRC.
On the Airbus products it is possible when using CI=0 or low CI values that the speed will be very close to Green Dot or when operating at the top end of the altitude/weight/temp envelope.
I have had a chance to view a lot of different Flight Planning Systems and CFP's and have not seen what yet that was planned based on Green Dot for the Airbus products.