CALYPSO,
I think that the answer is in the bottom line of your post
".......econ climb and econ descent should roughtly equate to best rate of climb/ best glide speeds. In my A/c climb is usually 285kts but descent 255."
Best glide range speed is Vmd and for jets best rate of climb speed is faster than Vmd.
Using your figures, if 255 Kts is Vmd then 285 Kts is about 1.12 Vmd. These figures fit the general theory.