Hi. I think @Joey_van_der_Gaag is exactly correct. The “piece” that may be missing is this: The reason you were able to achieve 79Mb/sec with Speedtest.net is that this service uses multiple streams. Therefore it is possible all WANS were in use and the throughput was summed across those WANs. The reason you were able to get only 19 to each of two computers is that no summing was taking place as there was likely a single session in play from/to each machine.
The reason you’d need a second Peplink device for “speed fusion” is that this feature operates between appropriate Peplink devices (or services). There are a number of whitepapers and “explainers” on the Peplink web site show how this works. The 2nd such device (or VM/instance) would typically be located in a data center with network sufficient capacity. See Virtual Appliance for Large Enterprises FusionHub- Peplink .
Does that help?