I have no experience with APIO. I'll presume you mean Balkan OI by BOI, and not Baltic OI (I have experience with the former only).

In my opinion:

For a gold medal IOI > BOI = CEOI

For any medal IOI < BOI = CEOI

I've only participated in one CEOI, but it seemed to be very similar in format and strength to BOI. The thing with these competitions is that often there aren't too many participants and it may happen that almost everyone participating is fairly good. On the other hand, on IOI you are guaranteed that there are some crazy good people, but also guaranteed that there are some people who have next to no experience with competitive programming. Thus scoring a bronze on IOI is generally easy, but a gold is really really hard.