strawb,
range is really dependent on the environment you are in and if you have interference (radio masts, cell towers) around....... also low batteries may effect range.....
best way to test range is get someone to hold your car.....then turn the wheel (no throttle) and hold it there.....now walk away until your friend lets you know the wheels have returned to straight....that will be a sign that the fail safe has kicked in and that will be your max range