The OBi router throughput is 30Mbps max. This is in the Admin Guide.
The only reason for the OBi QOS is if you use the router. And I would only use the router for some niche reason.
The only tweaking of the OBi that might speed up the Ethernet is to change the WAN/Internet port from default (2) 10Mbs half-duplex to (1) 100Mbs full-duplex (undocumented?):
Dial *** for Device Configuration Menu
Dial 0 for option
Dial 27# for current value
Dial 1 to set a new value
Dial 1# for new value 100Mbs full-duplex
Dial 1 to confirm/save
Hang up to reboot automatically
If you just plug the OBi into your router, I would switch it to Bridge Mode and have your router assign a static IP address for your convenience:
LAN Settings - Lan Settings::OperationMode = Bridge
Submit
Reboot
In Bridge Mode, the OBi is a 3-port switch with 1-port internal.