The faster the drive spins, the faster the head can potentially be over the sector it's looking for. Assuming the heads also move faster, this results in a lower seek time. Solid state drives are even better at this because there are no moving parts. The access to Flash memory is on the order of microseconds instead of mere milliseconds like even the fastest hard drives. The transfer rates should be pretty close as those are generally bus limited, assuming the data on the hard drive is sequential, of course.