Regarding GMTs, the 1675 is a classic, with the big lum markings, and by now original dials have a nice patina where the lum has usually turned a beautiful cream color. However, you have to the be concerned about condition and looking for ones that haven't been polished dozens of times to the point of having very rounded edges on the lugs, is the dial original or a later service dial (service dial reduces the value and on some level collectibility, some people love the curvature of acrylic crystals while others prefer the more rugged synthetic sapphire, and will the lack of a quick set date and lack of an independently adjustable hour hand (in place of a quickset) be an annoyance?
I like the 16710s. My father had one for several years. Its a good solid watch with the final changes/upgrades prior to the ceramic bezel models. If you want a sort of interesting one, search for a late Z serial or an M serial. These last versions of the 16710s are supposedly the only ones to have the newer cal 3186 with blue parachrom hair spring rather than a 3185 (although that's a good solid movement that powered many GMTs and Explorer IIs). Your also get an SEL bracelet (rather than clam shell ends on older bracelets) and an independently adjustable hour hand (which can be used as a form of quick set for the date).
As for the WG Pepsi GMT, I tried it on and its very nice. However, I've owned a WG Rolex, and I lost interest in it quickly so I'd never do another. It wasn't different enough from steel (yes some say its a stealth luxury model), but it looked so similar to the steel version of the same watch, that felt like too much $$$ tied up in a watch that didn't look different enough from my steel version. If I were buying gold I'd want a model in YG or RG so I could at least see the difference between it and the steel model, or platinum which feels incredibly heavy, and is more rugged than gold, and which when polished doesn't lose much metal as gold. Also, I haven't checked in years, but Rolex used to always plate their WG with Rhodium. I tend to keep watches for a long time and I wouldn't want to have to deal with the hassle or replating at some point.
Good luck with your journey to finding the right GMT
Thanks for your thoughts. WG Pepsi is definitely not an option right now. Though I thought I would be set on a Coke bezel, after seeing the WG Pepsi now I'm vaccilating between a Coke and a Pepsi.
I guess I will have to trawl the local pre-owned dealers to see what they have available.