XFi wired connection slower than wifi

Hi,

     I currently have an internet plan for speeds up to 600mbps.  I understand it is unlikely I will get that speed.  However, my iPad on WiFi gets around 500 while my desktop can only manage about 240, half as much, on a WIRED connection.  The NIC is 1Gbps capable.  On Windows 10, network status is showing 1000/1000 Mbps link speed.  I bought a brand new Cat-6 cable and it makes no difference.  From reading other posts, my CPU is NOT overheating or anything.  I have reset the XFi cable modem, restarted the PC, made sure the driver for the NIC is up to date and still no luck.

    I have also switched ethernet ports on the XFi cable modem.  How can I get speeds on my desktop to be similar to those on my iPad?

Thanks,
Rich