I came here looking for speed comparisons, after reading the post, I did my own test. I tested the speeds of FireWire 800/FireWire 400/Gigabit Ethernet.
So I think the NAS with gigabit is the best way to go. It allows expandability to a network or just connected via a ethernet cross over cable to one station. Gigbit is really cheap now, I picked up a 8 port gig switch for under 50 bucks.
Workstation: G5 2.7 Ghz, 4GB DDR SDRAM, Mac OS 10.4.5
Local Storage: Internal SATA disk 234 GB HFS+ Journaled and LaCie d2
150 GB HFS+ Hard Drive Extreme with triple interface USB 2.0,
FireWire 400, FireWire 800.
Network: Cat 6, Linksys SRW2016 16-Port 10/100/1000 Gigabit Switch
Server: Xserver 10.2.8 Dual 1GHz, 2 GB Memory with internal ATA and
SCSI RAID 5.
File: 1 GB Photoshop PSD file.
Workstation internal SATA disk to server ATA disk-29.5 sec.
Workstation to external disk via FireWire 400-29.8 sec.
Workstation to external disk via FireWire 800-17.9 sec.
Workstation to external disk via USB 2.0-1 min. 2.6 sec.
Conclusion: Gigabit Ethernet is dam fast, USB 2.0 is dam slow
compared to FireWire 400 under my normal and typical working