Step Turn
There is no such thing as a 'fast lane'. On a motorway, certainly in GB, all lanes are equal.
"doing a STOL takeoff".
Safety of this manoeuvre is surely conditional to the type of a/c being used. If you're 'driving' a STOL a/c then one is using it according to its design function. With for example, leading edge slots or slats, it is designed for steep departures and arrivals according to the topography.
The point that perhaps you intended to make was, that any a/c used for a purpose well outside that for which it was designed, is asking for trouble.