That's only in the anime.
If anything, the scene with the Kraken is proof that Sanji is faster than Zoro, since he attacked first.
Luffy is obviously the fastest after he learned Gear 2.
Zoro is not the fast type. The speed of his sword attacks is based on his technique. It's like comparing a 100 metres sprinter with someone who can type on a keyboard really fast.
Geppo is based on speed, you have to kick the air very quickly.
It's the sort of thing that Zoro would never be able to do, for example.
Example?