If Sanji defeats King or Queen, it will be more impressive imo because he did not show any capability to put him to same tier with commanders so far. He was being manhandled by Daifuku previous arc and him leaping to commander levels is an amazing feat on his part.
However, the question of whether he will fight commanders, Tobi Roppo, Daifuku, Perospero or anyone in this arc still remains a mystery.
Don't get me wrong, Zoro's feats and capabilities are beyond amazing. However, it comes down to expectations for me at this point. If he does defeat a commander, Sanji will pass a harder threshold in my eyes, because, after all, we all expected Zoro to be effective against Yonkos due to his part in story and his previous feats but Sanji showed nothing comparable up to this point.