Here are some test conducted with H2testw USB 3.0:
Writing speed: 94.5 MByte / s
Reading speed: 191 MByte / s
H2testw v1.4 (MSI GT72 2QE Machine)
Here are some test conducted with H2testw USB 2.0:
Writing speed: 27.4 MByte / s
Reading speed: 30.1 MByte / s
H2testw v1.4 (Machine HP Compaq 6000 Pro)
In short a good USB 3.0 key that works very well in 2.0 too.