I'd go RAID 5 if I were you too.
I have 3x 80GB.
One, my WD WD800JD, is my Windows & Apps & Games Drive
Two, my Seagate Barracuda, is my 70|2|23/\/7 Drive, this drive also houses my "My Documents," cause you can change the location of the actual folder to point somewhere else. My Documents houses my pix, music, and other stuff. THis drive also holds little apps with no installers like A64 Tweaker, etc.
Three, my Hitachi DeskStar is now a network-wide shared drive. Houses drivers, software, backups, and such, among our four-pc home network.
In total I use (not counting network drive)
36.14 GB HDD Space. Including the network drive (which also houses ISO's and Recorded TV), 45.88GB total.