Certainly a difficult one to answer looking at any Rolex or other high end brand right now.
Pre covid it would have been snapped up at 9.5k,knock possibly 2k of that now,and still hang around even so.
I have 2 16600s and although considered selling I just dont like the prices they are going for tbh.
Ill probably try a trade or straight swap for several lower value watches,preferably a Speedy in the mix.
Your friends watch does look very nice with the patina on the plots.