the result is just amazing!!
Are you managing to obtain this level of performance with RPi3 only (running in the same time ArduCopter and GStreamer)
Last time I tried my drone was very sluggish so I had to install a RPI Zero dedicated to the video streaming 
Did you connect your usb 4G routeur directly to the RPi or are you using Wifi on the drone? If yes could you please tell the “protocol” to be followed? I have read some articles that all use sakis3G which seem to be outdated.
As I am using a 4G Wifi routeur plugged on the RPi3 USB port to set a local wifi network on the drone. The result is a local wifi network (not connected to the internet) for my RPi Zero, RPi 3 and GCS.This is quite convenient to avoid using 4G for all flights… and less complex to set-up! 
but the range is quite poor…
I wonder if this would be possible to avoid having a Wifi dongle on the RPi Zero and connect directly to the local network through the USB 4G Key. I would save same weight in wifi dongle and USB cables.
I would as well prepare to switch to 4G streaming and telemetry for long range flights.
Thanks very much for your amazing posts… You just have realized my drone dream!!
Guillaume