8 Parts thus far and the combined some of their total length makes OP look short. You'd probably find it easier to get through by just watching the anime though, seeing as how it covers the first 4 parts in 113 episodes, covering 39 volumes of material (minus the omission of a few minor events. Two omissions do lead to plot holes in the anime's first season, but nothing story breaking). Part 5 is probably the weakest Part of the manga and Part 6 whilst having a lot to like, does feature a few flaws in it's semi-episodic structure, so I wouldn't say you need to rush to them anyway. Part 7 is set in an alternate universe, so if you want to get to the peak of the series quickly, it's fine to jump into it without having read most or any of the other parts.