Bern already has the greater career, the only question at this point is peak. Bird had a run of 3 years where he was arguably the best player in the game. Bird's peak was 84-85-86 when he won his 2 FMVPs and 3 MVPs.
Outside of that he was all-star great and even all-NBA great, but not all-time great. All-time greatness is established in the playoffs. Outside of that 3 year peak, Bird's highest playoff PER was 21.8 in '87 and his highest playoff WS/48 was .198 in his second season '81. In total for his career, including his 3 year peak, Bird had two postseasons
> 22.0 PER and two postseasons
> .200 WS/48.
In 9 career postseasons, Bern has had 9 postseasons
> 23.0 PER and 6 postseasons
> .200 (as well as seasons at .187 and .198).
Career advantage: Bern
Peak?
Bird top 4 playoff PER:
'84 - 26.3 (FMVP)
'86 - 23.9 (FMVP)
'81 - 21.8
'87 - 21.8
Bird top 4 playoff WS/48:
'86 - .263 (FMVP)
'84 - .236 (FMVP)
'81 - .198
'85 - .155
Bern top 4 playoff PER:
'09 - 37.4
'12 - 30.3 (FMVP)
'10 - 28.6
'13 - 28.1 (FMVP)
Bern top 4 playoff WS/48:
'09 - .399
'12 - .284 (FMVP)
'13 - .260 (FMVP)
'10 - .242
Bern's peak has been ridiculously higher than Bird's (not to mention Bern plays in an era where defenses are allowed to play 5-on-1 while offensive players aren't allowed to attack defenders in the paint).
24/7 media has us all well-aware of the single sub-par (for him) playoff series of Bern's 11 year career when he put up 17.8 ppg on .478% shooting vs Dallas. How about Bird? Has he ever had a disappointing playoff series to end his team's season?
'82 ECF loss to Sixers -- 18.3 ppg on .412%
'83 ESF loss to Bucks -- 18.7 ppg on .441%
'87 Finals loss to Lakes -- 24.2 ppg on .445%
'88 ECF loss to Pistons -- 19.8 ppg on .351%
If you aren't a fan of numbers because you hate science, simply youtube some espn classic Boston Celtics games from the 80s and actually watch Bird play. He was a streak shooter who relied on mismatches to get easy buckets down low (Bird was a PF playing SF -- McHale guarded opposing SFs while Bird was typically guarded by opposing SFs). Bird was a great player, obviously, but as a man of science and a high-level expert historian of the game, I just can't include Bird in the highest tier of all-time greats.
Tier 1
Jordan, Kareem, Bern, Wilt, Magic
Tier 2
Duncan, Shaq, Bird, Russell, Olajuwon