These are merely arbitrary numbers equating the characters on numerical values so as to come with a quantifiable measure of how to group them. In no shape do I intend to convey the message that the differences in one group to the next. This doesn't account for experience or match up disparities that occur and neither does it measure individuals with Rodger as the benchmark lest this list looks vastly different. Personally I prefer a letter based system but OP mentioned something about Rodger/WB being 80 which I disagree with. From portrayal Oda has hinted a lot Rodgers Era as a whole in their hey day is the single best era power wise in terms of quality. The forthcoming era had quantity and Luffys's generation has both quality/quanitity. Anyway as for BB without following any order I think
SS: 100
Rodger / WB / Pandaman
S: 97+
Garp / Shiki / Dragon / Rayleigh
A+: 95+
TS Shanks / TS Akainu / Old WB / Kaido / Aoikiji
A: 93+
Blackbeard / Fujitora / Ryokogyu / MUM / Mihawk
A-
Old Garp / Old Rayleigh / Old Sengoku / Marco / Marco / Jozu / Yonko Commanders