The difference between 7200rpm and 5400 can sometimes be 1 watt or more. On a 10 watt total power draw (13") that can be 10%.
If your battery life is normally 360 minutes that would mean 36 minutes difference.
http://www.tomshardware.com/charts/2009-2.5-mobile-hard-drive-charts/Workstation-Type-I-O,1128.html
Al depends on what MBP, what hard drives and what usage we're talking about.
This review does a good job of showing the real world differences between 5400rpm, 7200rpm, hybrid and SSD.
Hitachi 7K750 750GB might be a good drive for you. Good performance and I expect it's a bit quieter and to use slightly less power than WD Black.
Myself I'm very happy with the 500GB XT Seagate hybrid drive.
🙂 Won't work in a notebook. It uses a different interface and power supply.
16.4 seconds when it's cached: http://www.youtube.com/watch?v=ilB79hv6bfgI might consider a hybrid. How fast is your bootup time?
Is there a difference between 16/32MB cache? Will it affect the battery life? If so, by how much? Thanks
16.4 seconds when it's cached: http://www.youtube.com/watch?v=ilB79hv6bfg
A good 7200rpm drive usually has 16MB cache. It hardly affects battery life.