Dell Notebook Hard Drives (from Dell's site):
5GB - 4200 rpm, ATA-5 (ata-66)
10GB - 4200 rpm, ATA-4 (ata-33)
20GB - 4200 rpm, ATA-4 (ata-33)
32GB - 5400 rpm, ATA-6 (ata-100)
At first glance, it looks like the 32GB HDD would be the fastest, with the 5GB being the second fastest, and the 10GB and 20GB bringing up the rear. However, Dell specs. all these drives with the same seek and latency times! (17ms latency, 13ms seek.)