With the old fixed gear setup 30mph for gear might be about it. With
the newer more streamline gear, it is less. Retractable gear is an
anethema. It needs to be tested, annualed and repaired and the pilot
needs to remember to deploy it. It's unavoidable on some planes, but if
you can get by without it, do so. Your life will be a lot easier. The
faster you go, the more retract will gain you, that is true. On a slow
airplane it's not much.