Back in the Arlong arc, we saw Sanji fight against Kuroobi and his Fishman Karate. On land, they were about even until Kuroobi made the mistake of pissing Sanji off. Underwater, however, Sanji couldn't fight Kuroobi at all. Kuroobi had every advantage underwater.
Now, here we are, getting ready to go to Fishman Island. There will (more likely than not) be Fishmen superior to Kuroobi in skill there. There is also a high chance any battles that take place will be at least partially underwater (since Fishman Island is seemingly underwater).
So, my question to all: Do you think Sanji would fare better now than he did before in an underwater fight with Fishman Karate?