To me they can feel a little bit too close to call in term of peak goal scoring ability and result, 94 playoff Bure was really good, from 1986 to today, 1996 Sakic and 1991 Kevin Stevens scored more goal than him in a run.
All-time as said just above, consistency with similar peak, unfair or not, make it really easy to give it to Bossy. he won 4 cups scoring 61 goals in 72 games.
It was a bit of a low parity era but if we look only against solid playoff teams during those 4 years (boston, buf, edm, rangers, flyers, vancouver), he scored 43 in 49, that high level playoff hockey, good competition and scoring at a 1goal per game.
They both have spectacular intl resume, spectacular pre-nhl goal scoring, when it come to score a lot of goals they already did and everywhere when they were able to play, Bossy did it more and in a row.