niner, I really think you should keep that Big 5 to go with your Mamba. It is always good to have an easy bow to shoot that is nearly the same as the heavier one. When we start radically mixing things up is when the computer gets cross wired. I would bet that if you would only shoot the Hill longbows your form will modify into them. Today, I shot at only 18 yards and worked on only one thing, which is three things in one- anchor deep, release, follow though. I suspect that I am no different than most Hill shooters, the final part of the shot needs to be maintained to keep it all tight. It is much easier to do that with a like bow, it helps instill reliable muscle memory. I see that you listed an inch spread on your draw lengths that will settle in on its own, your draw length is was it is and it can be fractions over and under a whole inch. What I like about wood arrows is that it is much easier to find a spine that allows net of bop net arrows. Of course, until you know what that should be, it is best to not pick a number. If I had a 28" draw I would be shooting 70" backset bows as well, but I am just a tad short in the arm for that, the bow string wraps around my chest.