Theoretically running in modem mode should give a faster speed than in router mode based purely on the fact that in router mode the 'box' is doing a lot more work, packet filtering, NAT, handling wifi etc, all of which it doesn't do in modem mode.
However, in the real world you can find that the differences may not be noticeable, depending on what the underlaying actual internet speed really is and what the rated sustained throughput of the hub is. For example, if you had a 100 Mb/s connection, then the hub should easily have the ability to process and pass traffic at that speed without slowing down, you probably won't notice much difference. Kick the speed up to 500 Mb/s though and the hub could well struggle to sustain that throughput.
Of course wifi is an entirely different matter and there are so many variables that trying to compare speeds and get valid results is all but impossible..
I did power down the hub and leave for 2mins before rebooting.
yes you do need to do that when in modem mode and changing from router to PC for testing the problem with the PC is MS stupid Automatic Private IP Addressing that is a waste of IP space so when the hub is up and ready you likely have to unplug replug the Ethernet cable to get DHCP to work.