Is a class 10 card always better than a class 6 card?

If my device only supports the “Normal Speed” bus, will there be any differences in performance between the class 6 and class 10 cards. I.E. Does a class 10 card also garanti class 6 performance for streaming data

When it comes to Radom Access data, I could expect that a class 10 card would perform better than a class 6 card, even though if the device only supports the “Normal Speed” bus. Is this correct?