Brady might be the greatest QB of all time already; he's certainly in the top three of all time.
I think folks will make the Peyton argument and from a regular season perspective, they have an argument. The thing with Peyton/Brady and the regular season that most people don't realize is that Peyton has three more seasons under his belt than Brady. If you do out the math, Peyton still has better per/season stats than Brady... but not by much at all.
Peyton goes DIRECTLY, does not pass Go, does not collect $200, DIRECTLY out the window as soon as you add playoffs into the conversation. The numbers aren't even close. Brady absolutely SMOKES Peyton.
Most folks will still go Montana as the greatest ever.... and that's why I was saying "before he's done" because if you take a look at Montana's actual numbers and lay them up against Brady, they are pretty damn close.
Montana and Brady have each played 23 playoff games in their careers. Brady is 17-6, Montana is 16-7.
Montana: 5,772 yards Brady: 5,629 yards
Montana: 62.8% comp % Brady: 62.5% comp %
Montana: 45 TDs Brady: 41 TDs
Montana: 21 picks Brady: 20 picks
Brady has about 60 more completions but you can argue that either way... Brady completed more passes and was a bigger part of the offense (521 comps out of 833 attempts vs 460/733)... but Montana obviously had a higher yards-per-pass number (12.5 vs 10.8 YPP in Montana's favor)
Brady was the starting QB for 11 seasons and made the playoffs 10 times.
Montana was the starter for 13 seasons and made the playoffs 11 times
Brady has gone one-and-done twice
Montana did it four times
Brady 3/5 in Super Bowls with two MVPS
Montana 4/4 with three MVPs
I think if folks argued Montana, it would be tough to disagree too much.
... but Brady ain't done.