Those velocities are amazingly close. Pressures must be close to max.

The size of that case should be much more efficient with a heavier bullet.

I would not be surprised to see 185's hit almost the same speed at 165's, and 200 not too far behind. Different powders might have to be used, though.

I suspect a steady progression in efficiency all the way to 300gr.RN's.

Too, the fpe should also increase, showing that efficiency advantage.