I did a little exercise a few days ago. I looked at Montana's and Brady's careers. I applied a score to each season that is the number of games left to be played when the team won their final game. For example, if you won the SB the score would be zero - there are no games left to be played. If you won the conf. but lost the SB, your score would be 1 - the SB was still to be played when you won your last game (the conf champ). If you bowed out in the conf game your score would be 2. And so forth. The lowest score would be the most successful QB.
Totalling that up and averaging over the number of seasons played as a starter (so, less seasons off for injury), Montana gets 1.91. Brady gets 1.53. This tells us that, on average, Brady gets his team about a half game deeper into the playoffs each year than Montana was able to get his teams.
There is no doubt that Brady has been measurably the more successful QB over his career. And for longer; Montana had 11 scorable seasons. Brady has had 15 - so far.
I'll do some more later. Bradshaw, Kelly, Marino, Aikman and the Mannings will be easy. I'll add Unitas, Starr and Graham if I can figure out how to fairly compare the pre SB era playoff structures.