So, I decided to upgrade my "100 GB" drive to a "200GB drive". Both the original and the replacement drive is a Seagate, and both carry the "Momentus" brand. The principal difference, outside of having double the capacity, is that the new drive is a 7200RPM model and the old one is a 5400RPM drive.
I agonized a little about having a higher RPM drive because the principal downside is that to spin a drive 33% faster presumably consumes at least 33% more power. Given that the hard drive is the most significant consumer of kinetic energy (DVD drives spin a substantially slower speeds), I have to imagine my battery time must suffer when using the disk heavily.
But the upside is, I've got a much faster hard drive, and given that it's the only routinely used mechanical device to get access to my data (everything else is solid-state), a 33% improvement in rotational hard drive platter speed is going to mean much faster access to my data. And frequently, the hard drive is the biggest bottleneck in a computer. RAM has access speeds on the order of "nanoseconds", whereas hard drives are on the order of "milliseconds"... or 1,000 times slower than RAM.
But not only is there a 33% improvement in rotational speed (meaning access time to your data), the new drive has a 16MB cache, twice as large as the old drive's 8MB. To try to quantify (somewhat simply I admit) the performance difference, I used the handy unix utility "time" to copy one of my larger files on my disk (112,419,532 bytes). Here are the results of three copies each with the old drive and new, for your perusal:
% time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.666s 0:11.31 5.8% 0+0k 0+99io 0pf+0w %rm backup % time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.652s 0:06.02 10.7% 0+0k 0+5io 0pf+0w %rm backup % time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.636s 0:05.57 11.3% 0+0k 0+1io 0pf+0w %rm backup
% time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.367s 0:05.26 6.8% 0+0k 1+6io 2pf+0w %rm backup % time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.327s 0:02.01 15.9% 0+0k 0+0io 0pf+0w %rm backup % time cp ~/Pictures/iPhoto LibraryLibrary6.iPhoto backup 0.001u 0.326s 0:01.96 16.3% 0+0k 0+0io 0pf+0w %rm backup
In short, the new drive is 2-3 times as fast in copying a 112MB file. The laptop feels a lot faster launching applications, in particular, so color me extremely satisfied.