5 magical beast RHD, Large size, 21 strength and constitution, a trio of natural attacks, and improved grab with two of them? Nice. Animal-level intelligence, no reach, and a terrible equipment situation? Not so nice.
+0 or +1? I suppose the owlbear's rating could go either way, but I'd like to point out that it's possible for an ECL 6 character to already have an owlbear as companion (Beast Heart Adept), and don't recall people considering such a PC incredibly strong. With that in mind, I'm going to put down a +0 here.
Pegasi are next.