The base router platform is the same. So overall performance (eg router throughput @ 2.5Gps) is the same.
To be clear. A CAT18 modem in a HD2 or HD4 MBX can do 1.2Gbps down and 150Mbps Up in theory. The screenshot you show is confusing because it says CAT18 at the top and CAT12 below. .
We’d not expect 4 x CAT 18 modems working to provide 4.8Gbps (1.2 Gbps x 4) of 4G. At least not for many years because the mobile networks are not ready for that. Instead the 4 x CAT18 modems combined with Speedfusion give us the best possible chance of getting and staying reliably connected with a very good amount of bandwidth.
If you really want to be ready to do more than 2.5 Gbps of throughput then buy a EPX (30Gbps of throughput) instead of a MBX (2.5Gbps).
Because if you can be in a situation where a CAT18 modem on a desk next to a CAT12 modem will provide more bandwith and lower latency than the CAT12 using the same mobile network because the CAT18 supports more MIMO and higher levels of modulation.
In the real world, when you deploy a CAT12 in a location and get say 45Mbps, you can sometimes deploy a CAT18 and get double the speed all because of MIMO and Modulation improvements.
Reliability. You can use multiple connections from multiple mobile networks and bond them together with Speedfusion Bonding for packet level resilience and failover.