Luffy and him are roughly equal in strength during their fight, though Luffy likely has an edge when Arlong doesn't use water and vice-versa. As for Arlong VS Zoro, Zoro didn't reach his level until Whiskey Peak, with the injuries from his fight with Hatchan providing enough of a Zenkai for Zoro to make such a boost (since he even confirms such implications at Enies Lobby).
In terms of physical strength as in lifting feats and the like, he's likely superior to Luffy by some extent.