The 'speed' difference between those two drives, according to those reviews, are so close as to be totally irrelevant.
and this is where strange part comes in . why they are so close? way 7200rpm baracuda is not faster?
From the review:
"The Caviar Green range is designed to save power, so has a lower spindle speed of just 5,400rpm, compared to the normal 7,200rpm of a normal desktop disk. Western Digital has implemented caching algorithms designed to mitigate the performance reduction
that results from this."