I've touched the 6500km mark now with the original air filter. It still is in good condition. So I'd say 7k km with an original air filter can be done without worries.
Trying to source a good quality new one to get changed at the next oil change which is due in around 500km. Till yet found only at filter house which for 2500 is not good value for money.
About the average, we achieved 24km/l between the previous oil change. The car mostly did ring road tours, was like 1200km ring road and 900km city.