The best I've seen in my GTs was the other week, I put in £58 which equated to just over 51 litres, the trip counter was on 600.5 miles
Prior to this I was in the low 500's so I'm quite pleased with that given the milage I'm doing at the moment. Certainly a lot better than the 38 mpg my Chevy was doing
All I did was change my driving style a little and now get more mpg while keeping a few fizzy spells here n there lol