Download Speeds (200-350 MBPS) Significantly Slower Than Purchased Speed (1 Gigabit)

I have 1 gigabit internet service with Xfinity.  I have one device (a desktop computer) connected to the gateway via a Cat 6 ethernet cable with the network card running at 1 GBPS.  There are no other devices (including wireless devices) connected to the gateway.  Speed to the gateway is 1180 MBPS via the Xfinity app.  I am getting 200-350 MBPS to the desktop.  Measured performance with the standalone Speedtest app, the online Speedtest app, the fast.com app as well as the Xfinity speed test app.  Tried different browsers as will with no material impact.   I realize I will never achieve 1 gigabit in reality but this seems to be significantly slow when trying to control for a variety of factors and get the best result.  Appreciate any help or advice.