I want to say for modern pilots, the Breitling EVO, but that might be out of your budget, and not mechanical. I’d consider it for the features though.

Besides that, maybe the Citizen Pro Master Skyhawk, also not an automatic, but with some useful features for a pilot.

If you really want a automatic with GMT, I think your instincts about the Sinn 856 are right.

I used to wear a health monitor thingy on one wrist and my watch on the other. I forget the brand, but it was small and looked more like a bracelet than a watch like the AW.