Since Sanji has no goal related to strength and currently there is not a Eos enemy we can be sure of Sanji is going to fight, I have to resort his relation to Zoro and Luffy and the concept of the M3.
Sanji has always been part of the monster trio, which describes the three strongest member of the Strawhat crew, a concept Oda indirectly introduced very early in the story, demonstrated countless times and he never gave up on
And even though especially Zoro and Sanji insult each other all the time, they know they can trust and count on each other when necessary and they acknowledge the strength of each other too
And for the most part Zoro's and Sanji opponents have been approximately on the same level
And they not only try to outdo each other, they also
act as Luffy's left and right hand( I do not say they are)
I know some people often complain about using Zoro to put Sanji on a certain pedestal, but as I tried to elucidate
in my post, I think Oda emphasized that the gap between Zoro and Sanji is not huge, in some arcs it might be more ambigious than it others, take Skypia for example, where Zoro accumulated a lot of feats, but overall they are quite close, hence I think it's fair to scale Sanji based on how strong Eos Zoro is going to be.
As we know Zoro is at least going to be superior to the strongest Swordsmen Mihawk, which would place him automatically above Shanks and Fujitora, so to me the next in line would be the old legends as Garp, Sengoku and Rayleigh which do seem to be able to compete with top tiers, as seen when Rayleigh held of Kizaru, but ain't gonna win against them due to their decreased stats caused by their age...
This is how strong I see Eos Sanji is at the very least going to be.
Of course it depends on how much Zoro is going to be stronger than average top tiers, so Sanji could maybe end up as average top tier too.