I think, you will never know unless you try both in your room. They also have something called super black box, at least they used to have it. When it comes to cost difference, it becomes very subjective.
Top of the line models always get special attention, you may get better parts, tubes etc. Why not contact Octave and talk to them ? Maybe you'll get a better sense. There is a used Octave 70 SE for $5500 on Audiogon, by the way. With MC phono and black box.