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.