I would definitely go with the GMT.
A really classic, iconic watch, especially the 1675, though, as I understand it, you won't be able to change bezel inserts.
I would definitely choose the GMT over the IWC, especially considering you have the Dornblueth.
I used to only wear Panerais as I liked the size, the leather straps, and the dial faces.
I now dislike the size (way too big), and am not too bothered about leather straps (one of my five watches has a leather strap, the others are all bracelet).