Usopp's Strength

In my opinion, Usopp is the one Straw Hat with the most potential. As was shown in his battle with Luffy, Usopp can be incredibly strong, and now that he has spent two years training, he will be even better. I think that he will be able to fight opponents that are on par with Sanji and maybe Zoro, as long as he doesn't run away. The thing is, we haven't really seen much of his powers yet, so I was wondering what he will fight like. By the way, I didn't see him carrying Kabuto around, so does that mean he went back to his old Slingshot? What do you guys think?