Hey Josh
Welcome to Wetpixel!
I'm sure you'll get lots of advice and suggestions. Once you get to the high-end housings, like Nauticam and Aquatica (I'd add Subal as well) they are all pretty good with no real weaknesses. It can often boil down to personal preference and arguably peripheral issues. Which one do you like the touch and feel? Are any of them easier for you to get parts and service when necessary? Do you already have an investment in ports, extension rings etc which means moving from one housing manufacturer to another is an expensive proposition? It doesn't sound like it for you if you are moving from a Gx7 to an SLR.
If at all possible, it's worth trying to get your hands on your short list and just have a look at them. Perhaps at a shop or through a friend. Maybe even rent one or two for a weekend if feasible. Can you access all the controls you want? Does it just feel right in your hands? Do you like the colour! (why not!?)
Once you get into the SLR systems the "investment" gets pretty big and you don't really want to back a horse you might later regret. So worth, I'd suggest, looking around a bit and taking a bit of time.
I've moved from a Nikon D800 to the D500 recently and am delighted with it. I'm sure you will be happy with that choice.
Good luck with the search.