no more than it even is not less

The card makes about 4 MByte / s to be expected as Class 4. Naturally apply the usual criteria, for example, you copied vieeeele small files takes the "start file" "File Exit" much more time than copying the file itself. If you copy a single file which is very large to get to 4 MB / s. AS ALWAYS. Who achieved significantly better or worse results should inform times better as the technology works.
Little tip, go the speed at the beginning of the high data is written perhaps before they are "burned" on the media in a volatile buffer, then goes quickly down to the speed because the medium has to come afterwards?

... Man what do people expect at Ner 4 MB / s card that makes the 40 ??? ^^