But it's obvious that SATA III or a 6 gbps HDD provides better performance,data rate and access speed.
I don't think so. Access speed in HDDs is dominated by head-movement and platter-rotation speeds; putting a bigger pipe between the drive and the CPU won't make any difference at all. Data rate - maybe, in bursts, if the HDD has a cache. When the data is being read from the cache, you could get a burst over the max physical read rate of the drive. But unless you are reading the same 32 MB over and over again, this will have a negligible impact.