I purchased them directly from Mark Grants web page with around 1 week delivery. It’s difficult to say what the real difference was since Naca5 was sold before Chord so never did a straight AB test. But the Mark Grant going from Chord Clearway improved the bass and gave me sweeter more relaxed and neutral highs. Naca5 I mainly went away from since they are so stiff and it doesn’t work in my slightly tight/slim setup. As I remember them they were less neutral and a tad more “boomy” somewhere in the upper bass.
I went to Mark Green 6mm mainly because they are same shotgun style as Naca5 which should mean similar specifications but these are very soft and bendy. I also went with Allan Shaw (Harbeth CEO) recommendation to get as much copper as possible and forget about the rest. To me in my system that recommendation seemed to be true. Mark Grant cables to me are top notch quality for price paid. Had a friend changing from Chord Epic to the same and he told me the transformation was great in his system.