Also regarding the Ethernet connection, that should definitely be pulling the full speeds without an issue. The Sky Q Hub has much faster wireless than a N600 router and the ethernet ports support Gigabit.

Have you tested on more than one device ie tried with an iPhone 6S or something, holding it next to the router, and turning the wifi off and on before testing.

Are you totally sure another device is not using some of the bandwidth up?

I would expect 35 to 37Mbps on speedtests personally.