An example - I'm trying to find out how thick the new Panerai 562 & 564 are - and yet the information is difficult to come by and isn't even on Panerai's own website as far as I can tell.
Not good enough!
I actually take a caliper and measure the case dimensions and thickness myself, as even published statistics are imprecise. The currently produced Rolex Daytona ref 116520, for example, is listed as 40mm in terms of case size, but taking a caliper and measuring it from the standard 10-4 (not including the pushers) yields 38.5mm (@Belligero mentioned this long ago, but I had to confirm it for myself). Hence, it WILL wear smaller than a SubC / SD (which really do clock in at 40mm).
As far as thickness goes, I've measured the SubC ref 114060 at 12.5mm, the new SD4000 ref 116600 at 15mm, and the DeepSea ref 116660 at 17.5mm. No info for your Panerai references though. Sometimes you gotta do it on your own.
The choice for me is easy, as I am biased in 2 ways...I've never really liked the IWC Portuguesier and I'm a big fan and owner of a BLNR.
All kidding aside, in warmer weather/or a tropical climate I prefer watches on a metal bracelet. Most straps if worn in tropical climates have to be replaced more often than if you lived in a more temperate climate, particularly if you are outside a great deal (as you know sweat ruins or hastens the wear on straps). That being said, you could go with an aftermarket strap with a rubber lining, which might give you some additional wear from a strap.
For me the GMT is a very different and versatile watch. Obviously, if you travel or need to keep track of contacting people in another timezone the GMT function is very handy. You can wear it in all sorts of weather without worrying about the strap, you can wear it to go swimming, and other than for occasions that truly require a dress watch you can get by wearing it with a suit. Also if you go with a new or newish GMT you get a 5 year warranty or the balance of it, rather than a 2 year warranty. You mention living in a tropical area, and so I can't help but think that knowing heat, humidity and moisture are not watch friendly conditions there really isn't a watch I'd rather have for such an environment than a Rolex.
I would also ask if you have tried both on and if one made you smile more than the others. That can often be a more important factor than any advice we could give you. In the end, whatever you don't get this time you could add it to your list of "Must haves" for the future. Wishing you luck with whatever you decide.
Here is a quick photo to help you decide.