Hi,
We're running Windows 2000 advanced server with 6 Seagate Viper LTO drives via 3 2 channel Ultra 3 SCSI lvd cards. Our networker version is 6.0.2. We've been running with this config for about 4 months and put simply, the drives are smoking fast. The biggest limitation to how fast they write depends on your network and how fast the client can send the data. Our fastest servers (backup wise) have gigabit nic cards and can write to a drive at about 20-30MBps when they run simultaniously (about 4 servers). I have heard from our vendor that the quality of the media that you purchase can have a large impact on the stability of your backups.
Hope this helps!