6MT here.
Mixed 50/50 local/hwy 68L = Consistent 520KM with spirited driving everytime on highway. (Same route everyday for the whole tank)
600~620 if i cut out that spirited. And yes, I keep it under 2000rpm to obtain that number.
Achieving 700KM per tank is certainly possible if driving 90% highway at <2000rpm most of the time.
However, please do note that you are driving a sports car. Please don't mind the fuel economy
Enjoy the car to its fullest.
If you care about fuel economy, then you have chosen a wrong car, and should go get yourself a fuel saving car, or at least get one to offset the fuel economy