Pretty sure he Is at 5 for multiple reasons.
First of all a system that ends at 4 Is just weird. Even real bouties end at 5, with WB and Roger at 5 as far as Emperors go. Doflamingo's did It too.
Secondly, this system Is clearly a ripoff of Doflamingo star system. And what was the distribution? Let's see:
Do you see someting similar?
4 bouties of 3 stars/crowns, no one at 4 and one at 5?
Well, yeah, you get It.
Lastly, Akainu and Dragon are protrayed to be connected, and now both are heads of their organizations.
Dragon has 5b+ so It's very called Akainu has 5 (crowns) too.