Western Digital Black vs. Blue Harddrive Test

[betacase]

I have 4 Western Digital 640GB HDDs. Two are Black Editions and two are Blue editions. I placed the same 720p movie on all 4 HDDs and played it. When I skipped around I noticed no lag in jumping in the Blue edition HDDs, but I saw a slight lag in the Black editions. I expected the Blacks to be either the same or better than the Blues. So I tested all four with HD tune, and thought I would ask the community if this is to be expected for these HDDs or if my blacks are somehow below average.

WD6401AALS-00L3B2
WD6401AALS-00L3B2
WD6400AAKS-00A7B0
WD6400AAKS-00A7B0

I used HD tune to test each hard drive.

Results:

#1) WD Black

#2) WD Black

#3) WD Blue

#4) WD Blue

 

[sminlal]

There's nothing in those results to indicate any kind of noticeable performance difference between the drives.

 

[betacase]

Is there any other testing program I can use to distinguish if there is any real difference between these two types of drives?