Econet networking was first developed for Acorn's System line, which had a 6502 CPU clocked at 1MHz. It was later used in their ARM-based Archimedes machines with 8-25MHz CPUs, as well as the RISC PC line which pushed into the hundreds of MHz. So the system clock clearly doesn't need to be identical for all stations on the network.
There is, however, another clock needed on an Econet network: the network clock. This is a synchronisation signal transmitted to all Econet stations on the network, independently of data transmissions (which are carried on a separate pair of wires). System, Atom, and early BBC Micro Econet interfaces included a built-in clock generation circuit, but as only one clock signal is needed per network, it was removed from BBC Micros from Issue 4 onwards. The preferred approach was to generatle the clock signal with a separate device at the middle of the network, which was referred to as an Econet clock.
The frequency of the clock signal dictates the maximum transmission rate on the network. Naturally you'd want to use the fastest clock rate possible, but the length of your network and the processing speed of the connected stations will limit this.
In their 1984 Econet Installation Guide, instructions are given for varying the clock speed between 31kHz and 500kHz, mainly by changing the length of the clock's low phase (space) relative to the high phase (mark). Acorn recommend a maximum clock speed of 200kHz in this guide. They note that for a 500m network that value should be reduced to 180kHz, but that 300m the speed of the station hardware is the limiting factor: the Acorn Electron is specifically mentioned as requiring a slower clock speed.
In later years, with the introduction of the faster Archimedes machines, faster clock speeds (and transmission rates) could be achieved, but only if slower devices were removed from the network. One solution was to run a separate, slower network for old Beebs, and connect it to the faster network via an Econet Bridge.