Thanks for posting your question to the Sling Media Community. Ferguspa is correct, with speeds such as the ones you've reported, you wouldn't see a significant difference in performance if connected to the Ethernet port. The one potential benefit to an Ethernet connection is that it a slightly more stable connection than WiFi, but the M1 is designed to work effectively via either option. WiFi is definitely easier to manage, as the Slingbox does not need to be within a cable length's range of your internet router in order to connect with your home network.
Keep in mind, when away from the home location, it is important to consider the network speeds of your current location, as well as where the Slingbox is hooked up. As long as your network speeds at the remote location are sufficient, you shouldn't experience any issues. Speed requirements might vary depending on the device you are using to view your TV signal remotely. Here is a helpful article that breaks down the functionality of our SlingPlayer apps (including speed requirements).
Hope this information was helpful!