Chapter 1000 spoilers :
The guy will face Kaidou and maybe Big Mom along Luffy, Law, Killer and Kidd.
YES ! Killer isn't impressing at all.
But the two Yonkous means Zoro have a really high level.
So I would say Zoro was at least 3rd Yonkou Commander level starting Part 2 and he has to be not too far from 1st mate of a Yonkou now.
I think he could defeat Dofflamingo alone starting part 2, and maybe Cracker ( and Smoothie but we saw almost nothing of her).
And to be relevant now, with Enma, he is able to defeat any Scabbards in 1 vs 1 ( counting Sulong Nekomamushi and Inuarashi ) and he is able to face King equally.
🎼