As found in a player base on FTB Revelation 1.3.0 (FluxNetwork 1.12.2-3.0.2 / SonarCore 1.12.2-5.0.4), network usage is ~700 kB/s from server to client while in the area.
Using profiler, we can see ~8% CPU usage from Plugs pushing network updates, using ~8% CPU: