V6 Berlina speedo and fuel issues

Holden claims the Berlina will average 9.3 L/100 km so I would say yours is in the ballpark, but bearing in mind that is just two weeks old it should get a little better once it's run-in. As for the speedo, if it is showing a lower speed than the actual speed then it is illegal and you should take it back to the dealer to be fixed. The law allows the speedo to read as much as 10 per cent over the actual speed, but it can't read lower than the actual speed.