It's looks fine. You can't go by Explorer transfer time, which can be meaningless.
As already said, fragmentation can affect transfer rates. So can number of files.
Transferring between Cav Black 7200 rpm's, I typically get max 123 mb/s, but that's always a short burst. Average is about 57 mb/s. Average write queue length is 3, so the write side is bottlenecking. I'm surprised you get the rate you are, writing to a 5200 rpm drive. I expect it's big files.
Try using a stop watch and dividing to get your overall transfer tate.
Anything around 60 mb/s is probably good.