At what distance from magnetic north do pilots start referencing true north for heading? The Earth's magnetic poles are constantly shifting, resulting in a significant distance between the true and magnetic poles. This means that while using them as references for heading at lower latitudes makes sense, using them as such while flying in polar regions causes often unacceptable inaccuracy.

In a simulator, I noticed that many modern airliners have a toggle to switch between referencing true and magnetic north as appropriate; but at what distance from a pole would this toggle be activated?
In Boeing aircraft the default is to select MAG. When the aircraft enters the polar region it will auto switch to TRU. The pilot can also select TRU when outside the polar region.  

The polar region is defined as north of 82 deg N latitude or south of 82 deg S latitude. It also includes the region north of 70 deg N between 80 deg W longitude and 130 deg W longitude and the region south of 60 deg S between 120 deg E and 160 deg E longitude.