Consumption R350?

Hello to the round, we are interested in a R-Class as 350 gasoline. About consumption as far as the 320CDI is concerned, I have read several times. Does anyone have experience with an average consumption as far as the 6 cylinder petroler is concerned? Were yesterday in the DC branch. On my question how realistic the stated combined consumption of 11.5l is, the seller stated, with 16liter !! would one hit the point better?! In addition, the torque of the petroler for the 2, 3to eh too low and thus the consumption would automatically increase by high speeds?! Well, know the 350 from the W211 and find the engine basically awesome. With an approximate mileage of 12000km a year, a diesel less comes into question (at least as far as the ratio is concerned). Would be class if someone could advise me. Thanks in advance frauschnupp2