Both RUT240 and TRB140 have the same LTE Cat 4 modem, the difference being, that TRB receives its all computing power from the modem module, while RUT has a separate processor chip for non mobile functionalities. However, I would not expect a drastic improvement, as the amount of data received is highly dependent on the available bandwidth, and varies with the band selected, signal properties, weather conditions, base tower load, etc. Depending on the size of your mesh network, distance between the points, additional delays are introduced, which also add to the reduced performance.
A single 1080p video stream requires about 5Mbps, of available bandwidth, that is 20Mbps already for video data.
In comparison, RUTX12 has a few advantages over previous mentioned devices, as it has two simultaneously active modems, able to establish more connections, it uses carrier aggregation, which allows to increase bandwidth, and it simply uses faster, higher category modems.
In your case, the suggestion would simply be to test your scenario.