The USB 3.0 thumb drive is probably using faster flash memory to keep up with the interface, so it might be a solution, albeit expensive, even at USB 2.0 speeds. Bottom line is write speed. A fast read speed will do no good, and there are many thumb drives with fast read and a much slower write.
The solution of using a USB SD card adapter combined with a Class 10 or higher SD card has worked perfectly for me when using solid state memory instead of a hard drive.