Should also remember the more you use any flash storage media, it slows down and it slows down on thumb drives really dramatically. Because on flash media, you cannot overwrite existing data, it must first be erased. There is another issue with erasing too... While you can read and write to 4k pages, you can only erase 512k blocks.
But Windows can only transfer files as fast as the medium its talking to will allow as well as the max though put of the connection.