Having had the GX7, and EM1, and now the GX8, I'd say the GX8 is the hands down best choice overall (at least for me)
I personally hated the GX7 EVF and its 16:9 native ratio, which to my knowledge the GX80 retains. The GX8 on the other hand, has the best EVF of any mirrorless body I've owned, including the Fuji XT1, the Sony A7rII, and the E-M1. Its a huge 0.77x with no flicker or lag, and with no issues seeing into the far corners. Its simply one of the best on the market, and I personally love the flip-up design. While flip out LCD's do work for lower angle shooting, they can still be hard to see, especially in bright sun. So when your shooting action, dogs or kids running on the beach etc, being able to get that cool low perspective and still frame with a good EVF is a real winning combo, and a unique feature to the GX8
I also never found the GX7 comfortable to hold as I had to bend my index finger back to the shutter button. I find having the shutter on the grip, more DSLR style works far better for me, in the same way the A7II was a massive upgrade over my A7.
While the E-M1 is a great camera for the money with pretty good AF, I think the GX8, and likely the GX80, is faster, and at least with my Panny lenses, tracks action better with DFD. I can get a surprisingly high keeper rate with my Noctricon on the GX8 with C-AF.
Video is going to be much better on the Panny's too. No contest there, but the GX80 does give better stabilization for video over the GX8, so that is one point in its favor.
The real show stopper/deal breaker for me though with the GX8/0 vs the EM-1 is that lack of 'track pad' AF on the E-M1. I simply LOVE this feature. Being able to hold the camera to my eye, and use the LCD screen as a virtual trackpad to move the AF point around the frame just plain works. Its far better than a Dpad, and its even better than the XPro2 joystick. Its as fast and intuitive as it gets and when shooting fast glass, like the Nocticron or 75/1.8, it makes putting the AF box right over your point of focus effortless. I so missed it when I was shooting my recently sold EM1
I will say the EM1 has better IBIS, but at least for me, this isn't a real factor. Okay, I can shoot my 75/1.8 at 1/4th a second with the EM1 and maybe 1/20th with my GX8, but neither is really that useful for my typical subjects, which move. I have trouble with subject blur, not camera shake, 99 times out of 100, so while a cool feature, its not really solving anything for me.
I got an import model GX8 for under $800, and changed the video spec to 30/60P with a quick "service mode" button press. Fantastic camera for the money that I think is well worth chekcing out if your a m4/3 shooter. Its not the prettiest camera, or the smallest, but the design is really comfortable, super customizable, and with the big EVF and such its just enjoyable to shoot with