Lumix model differences

Though the model numbers support how you categorized them, in actuality it is different:

1. GX7, GX85, GX9 are really one series, and in fact in Japan the latter two are named GX7 mkII and GX7 mkIII. They are all about the same size, and all share the same viewfinder (though it does not tilt on the GX85). They all have a tilt LCD. The GX85 had some improvements over the GX7, but it also had some cuts in features to hit a lower price point. I have a GX7 and I was not tempted by the GX85. The GX9 is a clear upgrade over either the GX7 or GX85. In its favor, there are some amazing two-lens kit deals with the GX85.

2. GX8. This camera should really be considered a one-off, at least so far. It has a bigger body, bigger, beautiful EVF, and is weather resistant. It was the first camera with Dual IS. Though its four-axis IBIS isn't as good as the later five-axis IBIS in the GX85, G85, GX9, etc., it does OK. It seems to be becoming a bit of a cult classic, as it appears Panasonic may never release a true successor (the GX9 is a successor to the GX85, as mentioned above).

3. GX850 - a rebranding of the GF line. A smaller camera than the others, no EVF. I don't know as much about this one. It has its fans but never appealed to me.

4. GM5 - a little gem, supremely well built, with a tiny but usable EVF. To make it this small, they had to build a totally new shutter mechanism that is electronic shutter only once you go faster than 1/500. I think the GX850 uses that same shutter.