I say 6 or 7b, Roger was never the threat that Dragon is now.
Dude, Luffy pre-timeskip did better against WG than what the Revs are doing lately!
If Dragon had a bounty higher than WB, I'll call it BS with all respect.
Also, considering the the RIGHT HAND MAN of Dragon has a lower bounty than even Perosepro! It clearly tells me that WG bounty on Dragon will not be the highest because he's "world most dangerous criminal"
His ideals and views is what is viewed as most dangerous to WG. However, don't you think that if Dragon's bounty was that high (even higher than WB) that the WG would put more bounty on his right hand man?
I mean 600 mil? c'mon!
I have hard time believing it.
If Sabo's bounty was over the billion, then yeah, maybe. And you cannot tell me that they are not related topics. Because Oda himself answered in SBS that a Yonko bounty by default affect his subordinate bounty as well. If Dragon was that high, it would have influenced Sabo's bounty in some shape or form to be really really really high.
Calamaties and Sweet Generals bounty are also a proof of that