Hi.
Your internet speed is great, absolutely no problems there. The 2160p VBR profile in UI3 only requires about 3 Mbps of bandwidth as a maximum, and on a scene with nothing moving it will usually be streaming at less than 1 Mbps. Besides it looks like you are connected to UI3 over your LAN, not using the internet at all.
Therefore I conclude that the usage spikes on your Ethernet graph are not caused by UI3. Something else on your PC is using most of that bandwidth and creating the "up and down" spikes. That "up and down" pattern is typical of most video streaming services like YouTube, Netflix, etc, where they are buffering ahead a few seconds, then waiting for some of the video buffer to be played before filling it up again. By comparison a video stream from
Blue Iris / UI3 will be much more steady.
It is normal for Blue Iris to not be able to reach a full 30 FPS when streaming at 4K resolution through its web server. This is because Blue Iris is encoding that video stream in realtime and 4K @ 30 FPS is a very heavy computational load. Even a fast modern processor struggles with that because the load is not being spread across multiple CPU cores (and there's nothing you can do to change that).
If you were to change the streaming profile in UI3 to "1440p" or "1080p" then I think you would see the frame rate be higher and more steady. If you have an
Nvidia graphics card with NVENC support then it may help to turn on hardware accelerated encoding for the Streaming 0 profile in Blue Iris settings > Web server > Advanced. Configure the Streaming 0 profile and use the "Nvidia" option for Hardware Acceleration. In my experience the "Intel QSV" option does not work here.