Well Zoro has always been the most powerful crewmate, aside from Luffy. It's clear right from the start, and Zoro is clearly the "First mate" of the crew. He trusts Luffy completely from the start (once he joins), has the most ambitious goal next to Luffy, steps up when Luffy is struggling (Usopp fight, Zoro's words were powerful there) and Thriller Bark puts him ahead of the rest of the crew as well. While I'm sure there are going to be CP9-style skirmishes and Zoro and Sanji will continue to have little altercations and shown side-by-side taking out some crew members...Zoro is clearly the #2 of the crew in overall fighting ability. Which makes his power all the more interesting.