File Server: Mac Pro or xServe ???

We are a small office that will have about 8 people using the server. 4 of the users (windows) will just authenticate and work locally. The 4 other users (10.4 laptops) will be setup using mobile home directories. We also have about 300GB of data (pictures, word docs) that needs to be shared among the office members.

We need advice on the best hardware setup. Below are descriptions of what we think the config should be, but want to know if there is a better way to go without buying an xserve raid (too expensive). We would be open to an external RAID 5 3rd party solution if cheap enough.

I looked at the Mac Pro w/ RAID card. Figured I would configure it with 2 x 80GB (RAID 1) as the boot volume. Then use the remaining two bays for 2 x750GB (RIAD 0) which would store all the shared data, home directories and a folder containing all of our software in a dmg format. For backup I would have 3 firewire 800 drives with one serving as the offsite backup. Then one would be partitioned into 3 volumes where it would contain the last known working boot config, a test system for updates, and the 3rd for nightly backups. The last firewire drive will do incremental backups of the data volume which then gets swapped out for offsite backup.

We can also go the xserve route, but have to buy a Gizmac noise pollution case.
– 2 x 80GB (RAID 1 boot volume)
– 1 x 750GB for data and home directories.
– same backup method using firewire drives.

We will notice slowness running the HD and data shares off a RAID 1 from the Mac Pro? Is the xServe a better choice to have the HD and data off a single volume?

Thanks in advance.