To add to the example analysis provided by Frontier BV, the topic was kicked around a bit in an earlier chain of messages, with my summary of the state of affairs being in Live Event Streaming Setup.
Besides the backhaul capacity that Frontier BV is focusing on, there is the capacity within the cell management itself. For a review of that you may find “LTE Radio Load versus User Throughput” by Salo worth a read.
For a practical evaluation in a particular location - grab a bunch of LTE devices and run speed-checks on them, in singles, simultaneous pairs etc. to check how the aggregate throughput changes as the number of simultaneous connections grows.
One way that may be particularly enlightening is to start the speed check on one device, note the number as it runs, then start another, and then another, each time noting how (or if) the throughput on the first device changes as the number of locally active devices increases. Ideally, adding each device from a state of total non-connectedness (i.e., airplane mode).
And then, just for fun: run the speed check repeatedly on a single device, noting how (or whether) the numbers change from one run to the next.
As a local sample-set: In a particular location in Silicon Valley (Palo Alto) the speed varied ten-fold within a few minutes (from 2.4 Mbps to 27 Mbps) with the device sitting, unmoved, on a desk (an iPhone connected to Verizon). In another (the Sierra Nevada mountains - Yosemite National Park) the variability was less dramatic - three-fold (from 5 Mbps to 14 Mbps).
With that level of variability for a single radio, the multiple-radio experiments become more or less useless in the absence of other controls.
For the Sierra Nevada set-up some students have run a few experiments with Peplink equipment and SpeedFusion. Too early to draw any solid conclusions for that location and set-up (the antenna configuration is likely a more limiting factor than anything else in that particular scenario) beyond the obvious - SpeedFusion made the system more robust and adding radios did improve overall throughput (but not linearly - I’ll blame the antennas for now ).
So - it is complicated
Chat with your local Peplink Partner - I expect that they are the ones likely to be able to speak to the particular circumstances of your locations and available carriers.
Lets appreciate the experience and thoughts provided by the Peplink team, the good people at Frontier BV, Martin Langmaid, Marcus Dowling and other forum contributors. They provide advice and experience that our team has benefited from any number of times and in many ways.