I find this to be a great time to remind people:
Transfer speed means nothing when you're talking about the interface (SATA, PATA, DMA, UltraDMA, ATA6/5/4/3/3/1).
The only speed that matters is the rotational speed of the disk itself and the seek times. Sata's vaunted 3gbit transfer speed tells you nothing except how fast the controller chip on the hard drive's PCB can talk to the controller on your motherboard. In practice, your 4200RPM drive would go just as fast on SATA as it would on the ancient 40-pint parallel-ATA in mode 2.
It's like putting Z-rated racing compound tires (180+MPH / 300kph) on a 1990 Geo Metro (3cyl, 55hp, carbed). "Gee, why isn't my Geo Metro going so slow? The tires are 180mph!!!"
Next time anyone reading this goes looking to buy a hard drive, don't consume the hype about the interface -- look at the drive specs. A 10,000RPM Raptor on SATA 1.5Gbit will run circles around a 5400RPM Travelstar on SATA 3.0Gbit.