I tested it by formatting the FAT32, FAT and NTFS former and average speed that I have on multiple computers as Windows XP that Windows 7 is 3 to 4mb / s. To give you an idea, a functional USB key or USB hard drive to transfer of 20 MB / s when the system is not busy with other tasks. It is enough to slow the speed of transfer!
I advise you to refer you to a USB key EMTEC. I have a 16 gb which perfectly works without any slowdown. Perhaps we should prefer a USB key with less space but faster than the opposite!