USB3.0 flash drive - fast in vconsole.com 's tester, slow in actual use?

[VirtualLarry]

Trying to figure out why my USB3.0 flash drive, can do 40MB/sec write speeds under vconsole.com 's USB flash drive tester program, and when I format it FAT32 and write a series of JPG files (digicam pics), it slows down to 6MB/sec?