Great answer Matt, thank you for taking the time and detail to really address what I was hoping to find out. All in all it sound like the EVF is more than acceptable - and at least as good as the aforementioned Panasonic unit in the GX80 and GX7 before that. The 3:2 format I imagine makes a big difference too; the 16:9 in my GX7 frankly drove me batty on more than one occasion.
I do have one more minor and non-EVF related G1x question for you, however - one with regards to the low-light capabilities (or lack thereof) of the lens. I owned the early generation of Canon's EOS mirrorless, the EOS M - on which I used the relatively small 22mm pancake lens (a 35mm FOV equivalent) which was, in a word, superb - not just optically speaking, but also as a lens which was fast enough to use in some relatively low-light (or at least lower light) shooting situations. I still miss that lens, actually. Obviously with a f/2.8 zoom, the G1x won't be as good of a low-light lens as the f/2 22mm was; but all things are relative, I know. So my question (at long last) for you is: have you used it on occasion in lower-light shooting situations - and how does it perform?
That's actually something that comes up whenever and whereever the G1X is discussed. Let me first state that I really have an issue with colour (chrominance) noise - which is why I cap Auto ISO at 800 for both the LX100 and the GX80; the latter camera retains much more detail at that ISO, but starts to show - IMO! - objectionable levels of chroma noise at 1600, which is unfortunate because the camera's IQ is really impressive otherwise.
Now, the G1X III delivers equally usable, even better, RAW files at ISO 3200 than the LX100 at 800, period. And that's at twice the resolution. The GX80's RAWs is equal to, maybe a touch better at ISO 800 than the G1X III at 3200, but again, only offers two thirds of the resolutions. I use the G1X III at ISO 3200 without any real restrictions - though it has to be said that Auto ISO pushes the sensitivity to its set limit a lot of the time (meaning that I probably could reduce the number of images taken at ISO 3200 by changing the ISO manually more often).
What this means is that over the LX100 (my previously preferred compact), I get a solid two stops better ISO performance in terms of noise and detail, and that's at the pixel level, not even counting resolution; the latter means that if push comes to shove, I even get to crop heavily before ever touching the restrictions I see for the LX100. This voids the advantages of having a clearly brighter lens on the LX100.
Additionally, the G1X III's lens performs (slightly, but noticeably) better wide open than the LX100's, but I'd say there's not much in it scientifically. On the GX80, I can mount - e.g. - the Olympus 25mm f/1.8 and get better optical quality and even net a third of a stop better low light capability, but that means losing the zoom; as for the Olympus 12-40mm f/2.8, its IQ is visibly superior to the G1X's lens, but of course, the size penalty is considerable.
To put the lens' performance into perspective: During my Scotland trip, I shot the G1X III alongside the Leica M10 and, for some time at the beginning of the trip, the GX80. I retired the GX80 for the rest of the trip after a couple of days - I really like the camera, but the G1X III outperformed the combo I had brought while being a third of the size (and 25% lighter). Of course, I have to admit that I had brought an optically inferior lens for the GX80, but the Olympus 14-150mm II had me satisfied on other occasions (and, to be fair, performed according to my expectations again). On the other hand, I had (and have) no reservations whatsover about mixing results from the G1X and the M10 ... Of course, Leica glass is visibly sharper and generally delivers on a different level, and so does the FF sensor in the M10 - but I shot some of my favourite images on that trip with the G1X III, and if there is an IQ limitation (which, technically speaking, is bound to be the case), it doesn't appear to be decisive, nor was it holding me back at any time.
I think the sensor/lens combo on the G1X III is a win - but I definitely appreciate Canon's decision to go for compactness instead of a bright lens that would have had to be a lot bigger (or offer less zoom range). Furthermore, weather-resistance (I wouldn't dare thinking of this level of protection as "sealing") meant that I could, with some care, take images in rainy/wet conditions during my trip, but that's not within the scope of your question. What may be of interest, however, is my observation that the 22mm f/2 is an exceptional lens - the G1X's is just good, better than most kit zooms, but still a zoom, and less versatile than fast prime. A Canon EOS M body would give you access to a lens you already know you like - and it's certainly true that the G1X III is pricey, even considering its merits. I think a M5 with the 22mm is cheaper and the sensor is the same (though the processor is one generation behind - not that important if you work from RAW) - all while being not that much bigger. Apart from size, some convenience would have to be sacrificed (weather resistance, actually more controls), but you'd safe on money while gaining even better IQ.
M.