Hard drive - speed vs battery life

Seems like I've been waiting on the i5/i7 refresh forever now, but since there is absolutely no hints from Apple as to when (and if) this refresh will ever happen, I am close to submitting and getting the core 2.

Concerning the hard drive speed. I am trying to get an idea of which hard drive speed to choose. The only 2 variables is the performance versus battery life. Based on my usage (which is just simple home use, nothing too demanding), can anyone help me to determine the thresh-hold between the speed gained from going 5200rpm to 7200rpm versus the battery life lost? Obviously the faster HD is more appealing, but how much battery time would I loose? The computer is a 15" MBP 2.8ghz. Thank you.

I didn't notice any battery difference going from the standard 250GB 5200rpm drive, to a new 500GB 7200rpm drive. negligible, if at all, for me. 2.4GHZ 15" MBP.

Todays hard drives are so efficient, it's all but impossible to notice a difference in battery life. Of far greater importance is the speed you will gain, as your apps will launch faster, web pages will open faster, etc. Go for the 7200rpm drive. You will be happy you did.