Just a Reference for Speeds:
Fibre Channel
SAS
SCSI
Internal Sata
PATA
E-Sata
.........
Firewire
USB 2.0
..........
Ethernet
..........
USB 1.1
You can consider the gaps a relatively big drop, with each group being generally comparible, although E-Sata can be very much worse than interal PATA/SATA depending on the implementation. Firewire is generaly faster than USB 2.0
The top 6 are all comparible if done properly, but Fibre/SCSI/SAS drives obviously are the only ones with 15k RPM drives.