HDTune tests a similar level of features as compared with HDTach, but with a different access pattern. Thus provides us with an additional set of benchmark numbers to compare between storage configurations. Here we can get the minimum, maximum and average transfer rates as well as the burst rates and access times. CPU utilization has proven negligible with modern processing horsepower, and is no longer included.
All drives have little issue pegging SATA 6Gb/s on reads. The 512GB M550 saw an unexplained 10 MB/sec dip, also present in the 1TB model, more than likely due to addressing limitations of that controller that are amplified by this particular benchmark's method of access.
HDTune's random access test method was developed for HDDs and gives varied and unexpected results for SSDs. Posted here for information only.