Why are my ping times so different to the same IP address/domain name when I run a speed test (5ms) and command prompt (117ms)?
It likely is not the same IP. 5ms is almost impossible. It would have to be a server located very near your house and you would have to have a fiber to home type of internet to get numbers that low. Most people the first hop between their house and the ISP first router is close to 10ms.
Go into the network tab of the resource monitor when you run speedtest. You should be able to see the IP it is using. If it is a tcp session you can see the actual latency to speedtest server. Speedtest is a little strange though it will open session to mulitple server, not sure why......likely some advertising crap. You should be able to tell the testing server though because it will have a lot of traffic