i worked for a portrait photographer who shot weddings in the 30 / 40s.
she used 4x5 pre annys for candid shots and for the formals she used
her 5x7 speed. 5x7 was one of the ideal portrait formats, easy to
proofs, easy to retouch with leads and easy to enlarge.
probably after the war when color film was more commonplace ( and mf used more )
the need 5x7 speed graphics became a relic of the past.