are the tests wired or wifi always test wired - assuming you are take your router out of the circuit and test one pc wired direct to the hub - if thats still slow try a reboot of the hub and repeat - again if thats still slow then do a full reset of the hub - that will put it back into router mode so you will have to put it back into modem mode to test and add your own router back
if non of that helps
log into hub3/4 - 192.168.0.1 [or 192.168.100.1 if in modem mode] - DON'T SIGN IN, click - click router status [centre of screen] - and post the downstream and upstream figures - to see those press on the grey buttons/boxes labelled - upstream - downstream
Have tried your suggestions and at best I am getting anything between 490 and 850. The variation is quite something. This is direct from the Hub4 and then through the modemed Orbi router. Incidentally, that has a built in speed checker. It tests the wired speed into it, before dishing out to any of the devices. That corroborated a similar variation, with results showing at 940 thru 560.