The Class and UHS speed ratings define a minimum rate standard. Also there is no standard on how the speed of a card is to be stated. So a manufacture could be stating a theoretical best case speed or sustained write speeds.
For example the Sandisk Extreme SDHC UHS-1 compliant card has a read/write speed of 45MB/s and the Extreme Pro SDHC UHS-1 card is 95 MB/s read and 90 MB/s write. Yet a Lexar SDHC UHS-1 card has a read speed of 60 MB-s and write speed of 10 MB-s. All of them rated Class 10 UHS-1.
So there can be a large disparity with different manufactures reporting.