Xfinity App/PC Speedtest Conflicting Results, Random High Ping Spikes.

My plan is for 1200mpbs. Xfinity App shows around 1000-1200mbps, when running the test on my personal computer it only shows around 500. PC is hard connected through ethernet. Running the test over Wi-Fi shows around 300mbps.

Also having intermittent ping spikes that last for a minute or two, either reducing speed by a good margin or killing it entirely. Have had the conflicting MBPS results forever, the Ping Spikes started within the past month.