velocity is not a safe way to guage pressure

You should go back to the 65.5 gr. load and shoot it some more. Try to get a could read on the speed and group size. Anyway that is where I would start. Your speeds don't make any since to me. Was that an avg. of several shots? Your Chrono may have malfunctioned.

FYI, if you can get a 7 mag to shoot 160's anywhere near 3000 fpsaccurately you've got an awesome weapon.