Well, it finally arrived - and on the same day, so did the separately-acquired watch box and operating instructions from two other Ebay sellers. I am very happy with everything!
Rolex GMT Master II, Ref. 16710:

KerryP: After some time researching the GMT, I came to the conclusion that I'd not really given it a fair shake the last time I had one in my hands, close-to (coincidentally, when I was in the process of buying my Sub back in 2003). By all accounts, the case sizes are identical in width and height, excepting the crown guards. The guards (not to mention the Triplock crown and slightly thicker case of the Sub) is, to me, what give the Sub it's classic look. The proportions of the Sub seem just about perfect.
In the case of the GMT, I thought the proportion was off, but as I looked at more and more photos it looked more and more right. Confirmation of that was solidified as soon as I removed this from the packaging, and it's carried right on through wearing it on my wrist - and it's just that bit lighter and sleeker, which is nice for different activities (I think this will be on my wrist for most of my cycling now, for example). The functionality is the icing on the cake - and it's still rated to 100m, too!
The best part is that the particular one I scored looks virtually unused, with no stretch to the bracelet and no markings to the case or bracelet. Seems to be running perfectly, too. A most handsome and useful addition to my (now) 3-watch collection. Even came with a spare bezel insert.
Time for a double watch-winder
DD