On the other hand, an HDD with 7,200 RPM will have speeds of around 150MBps. A hard drive with a 5,400 RPM will have a speed of around 100MBps. A SATA III data connection is capable of a maximum of 600MBps transfer rate, but the RPM of the HDD determines the final output. The RPM rate of most hard drives ranges from 5,400 to 15,000. The higher the RPM, the faster the hard drive will be. The RPM of an HDD’s platter determines how fast you can read and write data. There are several factors that affect SSD vs HDD speeds. Hard drive speeds are measured in megabytes per second or MBps.