If you are sending files back and forth those are sequential(larger files will be faster, while lots of slower files will not be as fast. for the most part access times do not play too much effect.
It is not like loading games and stuff.
Again, for storage, I personally use slower drives(spindle speed).
If i NEEDED to be able to chew on fragmented files or jump from location to location lots(Windows/programs/games), then a 7200 rpm drive is your friend.
I do not see how the SATA 6gigabit/sec will actually help tho. I mean the drives buffer is about the only thing that will work that fast and those tend to be from 8 or so megabytes(laptop) and 16-64megabytes(desktop). Once you full this, you are fully limited by the drives actual mechanical limits(under SATA 3gigabit/sec).
The biggest thing for hard drives is that when they introduced PRM, drives could pack TONS more data on the same sized platters.
This is why you can get a 1TB laptop drive that fits into a 9.5mm thickness
.
By placing the data closer together, the drives get MUCH faster sequential read/writes. access times are the only thing that is truly holding hard drives back.
Think of 9-16ms access times vs ssds with 0.02ms(or less) average access times.
I remember my first 40gigabyte drive could JUST push upto about 40-50 or so megabytes a second if I remember right.
in 2007 I had 2 a 2 drive RAID0 that pushed 120mb/sec by 2009 the same number of drives pushed over 200. Now a single drive CRUSHES what was once fast.
Either way, I can run some benchmarks from SATA 6gigabit drives on SATA 3gigabit if you would like to see if it has any difference.