streetshot

I researched this some time ago. For Youtube (don't know about other services), the max allowed bitrate for 4k 24-30p is 35-45Mbps. Youtube, in turn, will downscale when they "process" your video. Numerous youtubers have noted that when you upload 4k and let youtube downscale, the results are better than when you upload 1080p 8Mbps. I concur on these results. In short, you want to upload to the absolute maximum that the service provides as those are the limitations of the service.
For Facebook, maybe try here:
http://www.macxdvd.com/mac-dvd-video-converter-how-to/best-video-format-for-facebook.htm
Also remember that Facebook declares ownership of anything you upload to its services... not nice.
Looks good, but unfortunately I refuse to use Microsoft Windows. Bummer... really want ffmpeg command...

use this
http://hdcinematics.com/Convert-V3.html

Yes, I've been doing the same with FCPX. However, my computer (integrated graphics) has a hard time with 4k with any sort modification to the original file. For now, I'm just testing as to what I can do with a downscaled image. I, too, am trying to improve workflow to make my cuts go a little quicker in FCPX, especially when 4k is not needed (rarely is).
When uploading to Youtube, you want 4k, even if it was originally 1080p- you only need to add a little grain and youtube will see "4k" detail. The results are pretty good from tests I've seen.

Yes. No problem. Put it in "M" mode and save it as a custom mode. You can adjust your aperture and shutter independently. I wasn't aware of the GX8 limitation...

I will say Panasonic does do some magic here. I've had cameras that produce a very digital line around anything blown out. Panasonic seems to render with a little more gradient (and grace) so that it's not as noticeable. The goal was to do "run & gun," not think too much about the shot. To bring her face out more, I would have installed a reflector had I thought a little more. But even then, it's all a matter of preference I think. Some people really like a darker image than others.

Nice write-up. To be honest, I actually quite like the blown out window arround 0:30 - looks natural to me.

The GX80 is meeting my expectations for run & gun. I think this shoot exemplifies expectations one can have of this camera for your quick, set-it-up and shoot style videos… family, street, etc.
Here’s my setup:

GX80 Panasonic 25mm F1.7 Zoom H1 Sony ECMCS3 Clip style Omnidirectional Stereo Microphone Settings:
GX80: Natural profile (Contrast = -5, Sharpness  = -5, Noise Reduction = -5, Saturation = -5), White balance (Sunny, A3, G3), ISO (200), Sutter Speed (1/50), Aperture (F2.8), IBIS (on, but no electronic IS) Zoom: WAV (24-bit, 96K Hz sampling), Level (70) Description of shoot:
This took me about 5 minutes to shoot. I saw an interesting opportunity, went to get the GX80 and Zoom H1 from my office. For the settings above, I only need to put the camera in “C” mode to start. The Zoom is always put back with the level at 70, I only need to place it near the subject and start recording.
Post Processing:
Imported sound from Zoom H1 (just connect, don’t take out card) - 30 seconds Imported video ~3 minute video file - about 3 minutes Synced files - 10 seconds Threw it on a 4k timeline - 1 second Expanded audio - 1 second Select camera audio and push “v” key - 1 second Added 1db to Zoom H1 audio - 1 second Collapsed audio - 1 second Make cuts - 10 minutes Color corrected (highlights = + 15%, midtones = +7%, shadows = +1%, Global color 110° = -3%) - 2 minutes Added FilmConvertPro2 effect (KD P400 Ptra, Grain = 0) - 10 seconds Added a simple title - 10  seconds Rendered video - ~20 minutes Total Post Processing time = ~40 minutes (with rendering)
Re-rendered video at constant bitrate of 35000 kbps in 4k with Handbrake, resulting file 690 MB- ~10 minutes
Uploaded to Youtube - 90 minutes
Youtube processing - 10 minutes
 
Final Product:
Picture Quality:
Hindsight is always 20/20. I think the scene was a little dark as her face falls into shadow from time to time. I probably could have bumped up exposure and just avoided the window blown out in the background, but it gives you an idea of the limitations in terms of dynamic range. For me, the colors are quite nice and pleasing after applying Filmconvert… before that, not so much as white balance was off due to keeping blue channel from going too low- I guess many cameras need to be tweaked.
Notes:
This is a video of my daughter trying to set-up a Canon Powershot A410 that I gave her. She practices from time to time and enjoys shooting. Capturing moments like this is one of the main reasons I bought the GX80 for family. Please excuse her coughing as she’s getting over the flu. Also, note that she’s constantly switching from English to French. Good luck trying to understand, but you still have an idea of the audio quality.
Of the video I cut out was a portion that was probably unusable as I wasn’t holding the camera steady enough as I moved to another position. Yes, it’s prone to jitters if the IBIS goes past its limitations, but I could easily have avoided this hadn’t it been to user error (movements were simply too fast).
Feel free to make comments on any of the above as I’m trying to improve everything! By the way, here’s a photo she took of me looking serious during this shoot. 

GX80 manual says the same... I don't know why Panasonic is doing that to us- then they don't tell us if it's 8-bit 4:2:2 or 4:2:0. I believe the GX80 one-ups the GX8 on that point because it will record internally at the same time. I would say both cameras are very capable. However, I believe this person is after value based on what he said... I'm going to say the GX80 beats the GX8 because it's less expensive. If he wants weather-sealing though, the GX80 is NOT the way to go- choose GX8 of GH4.
I just pixel-peeped it and still couldn't tell a difference. Staying with the original file.

Depends what's more important to you.
Do you want a mic jack, larger grip, fully articulating screen, longer battery life, slightly larger viewfinder, cine profiles, and $200 cheaper RRP? 
G7.
Do you want smaller size, a denser-feeling camera, a tilting screen, and the all-important in-body stabilization?
GX85.
From what I've seen, CineD provides no DR benefit over Natural. The only reason to shoot CineD (imo) is if you like the Leeming LUT workflow.
Actual image quality is identical between the two, so choose based on ergonomics, features, and price. 

Thanks to both of you for these responses...they help a lot!