Using 'Downwind' Gillan's effort as an example is a little unrepresentative, with a top speed of 328-335, getting an average speed of over 408mph would have been using full power or very close to it.
Once you've got over the initial panic, training takes over and you'd reduce throttle to loiter and think through your options.
A lot of pilots getting caught above a low cloud base headed east and then let down over the sea to try and get under with no worries about barrage balloons, et al.