To get 4k from the Rally camera, connect directly to a standalone PC via USB 3. Rally cameras record in 4k, but it depends on the application you are using whether it can record/stream in 4k.
With the Rally System it depends on where your room PC is located, you may not always see a 4k image. If your room PC is connected directly the Rally Display Hub using the provided cables (USB 3), you should have a 4k signal to your room PC. If you have the room PC mounted at the table and are routing video through the Rally System, bandwidth restrictions cap the maximum resolution from the camera to 1080p.
Other factors such as cable quality, network restrictions, and graphic processing capabilities may also affect the final resolution of the camera feed.