I say M3, mid-high diff. I think Sabo can beat them all individually but no easily since all 3 are so damn durable. Sabo would have to bust out some good moves and with all 3 having good Haki, especially Luffy, Sabo will have some trouble handling all 3 despite being a Haki beast and his new but very destructive DF. I think they'd be able to catch Sabo off guard at some point since all 3 have good speed too (so does Sabo of course). But for him to take on all 3 at once, I think it may be too much for Mr. Second in Command.