Thank you for the comments. Only Omarmuslim seems to be correct as he has at least bifurcated the mileage for the 2700 and 4600 CC car.
However, please note that people who buy these cars with "halal" earnings do tend to worry about the fuel averages. Sometimes you can buy these cars but have to drive them rarely because of the fuel consumption. I'll be using the car on a daily basis hence I'm concerned about the fuel consumption
Thank you for your inputs