cannon range: game vs reallife

[baldwin8]

Quoting Spitfire Pilot JD Lindsay from Robert Bracken's book "SPITFIRE II THE CANADIANS"

"I fired on a straggling 109 at the 800 yard maximum range with a 20 mm cannon and got strikes on the aircraft."

How does this range compare with the game? My marker for deflection shooting starts to show in just under 4000 ft to target. There have been lots of comparing aircraft, but little about game vs reallife weapons in this forum.