Cloud Backup requires the calculation of checksums. This helps ensure that your backups are efficient and complete as fast as possible.
The speed counter is an average counter and will be most accurate when backup is in the middle of a folder with similar file types. Smaller files will report slower speed since they finish faster and larger files report faster speeds. There is a greater disparity between this for users with fast upload connections.
There are sites like Speedtest to check your upload capability. The upload amount reported will help you establish an idea of what your connection is able to do. There are many factors in a connection that effect speed and this is just one of many ways to learn about your connection.
Below is an example of how Cloud Backup looks when calculating checksums.
Once in the middle of file transfer, you will see something like this: