Anyone managed to get more than about 230Mbps from an Aircard AC810 on 4G ?

I have an Aircard AC810 with the DC112A cradle and I'm struggling to get the throughput I expect from it. At best I can get about 220Mbps whereas I should be getting over 400. 

The device is connected to a laptop by an ethernet cable and is in an area with very good signal from three LTE bands each having 20MHz bandwidth (800, 1800 and 2600 MHz). 

Initially I had tried downloading from the internet and also using the Ookla speedtest.net site. When that failed to achieve the expected throughput I decided to use iPerf3 for which I connected a server directly to the mobile core network and downloaded from it instead of from the internet but achieved no improvement.  I have also tried using WiFi to connect the laptop (instead of ethernet through the cradle) to the AC810 but it made no improvement either.

I have confirmed that the setup from the mobile network side is working fine because with exaclty the same setup  but using a Samsung smartphone instead of the AC810 and the laptop  I can easily achieve 380Mbps and also quite regularly between 400 and 420 Mbps.

The Netgear on the other hand seems to be limiting to about 220 Mbps no matter what I do.

I have also checked that the two laptops have no limitiation as they achieve over 800Mbps when conencted directly together by ethernet cable and even when I connect both of them to ethernet ports on the DC112A cradle (using it as an ethernet switch) and transferring between the two laptops.

Given that the AC810 claims 600Mbps on 4G+ in the datasheet and that I have radio coverage good for 450Mbps shouldn't I get at the very least some 400Mbps, especially since I can get that even with an Android smartphone?  Has anyone manged to get over the apparent 220Mbps limit with this device?