Anyone who knows even a little about Hard drive hardware will understand what I wrote is true, dont whine just because some people know more than you about computers. I probably do appear intelligent given I have a masters in computer engineering, however if I offended your ego thats not the way I mean to come accross.
However here are some sources for more information for the Original Poster:
http://www.barefeats.com/hard80.html
http://www.tomshardware.com/reviews/fast-furious,1169.html
"On the other hand, as you see above, the power usage penalty is about 10% for choosing a 7200rpm drive over a 5400rpm drive while the latency advantage is 31%. Therefore, it could be argued that the lower latency and faster seek time means the 7200rpm drive spends less time working -- thereby conserving power usage."
Barefeats is quite good for random and hard to find benchmark comparisons, if you search around you'll find lots of comparisons proving my point.