Stewart, I love the GMT but only with plexi up, so only first excution models form '58
They are so light at wrist, sometimes with fantastic vired color of gilt dials and bezels.
6542 (the first model) with original bakelite bezel is stunning, after this, the 1675 OCC dial is similar but no bakelite.
They are the best of GMT's collection, after this you can see also the transitional 16750 matte dial, more young and not so charming;)
In the 1675 models you have a large series of dial, gilt and matte, but i love the first of two sometimes got a brown color or chocolate like sow
with gold letters.......they look very very nice ;)

GIGI