Upgrading the harddisk on a laptop is the single most effective way to improve functionally and speed on a laptop, it is the single most important component.
Not only is a new harddisk faster, it is larger so you could store more files, and not to forget the assumption that a new harddisk would last longer than an old one.
Here I compare the existing king of the hill 2nd generation 7200 RPM drive from Hitachi which is the 7k200. The upcoming 7k320 should be coming in a few months time. And the forth generation 5400 seagate drive the 5400.4 250G.
First are the benchmarks numbers
As you could see the forth generation drive from Seagate is pretty close to the 2nd generation 7200RPM drives. The reported numbers for temperature I assume is wrong as I felt the 5400 drive to be cooler to the touch compare to the 7200 drive. Maybe it is the way the position of the temperature sensor is taken .
I must say that the 5400.4 is very much faster than the 5400.3
In Windows experience index the 7200 drive is reporting 5.4 while the 5400 drive is reporting 5.3, previous generation 5400 drive are in the region of 4.7 to 4.9.
Conclusion if you are looking at an harddisk upgrade I would recommend the 5400.4 drives over the 2nd generation drive as the performance is pretty close at about half the cost not to forget the 50G of extra capacity and a cooler running drive.
Until the 3rd Generation 7200 drive is available.