Terms like USB 3.0 and 2.0 only refer to how much data the connection is capable of. The actually speed of the device is determined by the hard drive itself. It doesnt matter how fast the connection is if the device is only accessing data at a fraction of that speed.
Lets say USB 3.0 is a road with 10 lanes. and USB is a road with only 3 lanes. It seems like the wider road would be faster because you can move more traffic across it. However if there is only one or two cars moving down the road, it doesn't matter which road they take, one wont be faster then the other.
SSD hard drives are MUCH faster then traditional HDD drives. they can access data 5x greater or more. it moves data much faster then a USB 2.0 connection...