Let's talk about you budget? I mean, you could start using external arrays, specialized controllers, etc... but I'm telling you that a RAID-0 volume will perform so that you will likely never have a HDD bottleneck.
SAS drives are better, but they are backwards compatible with SATA drives. You would get a performance advantage using 15K SAS drives, but are really just using them as 15K SATA drives. Serial Attached SCSI is especially beneficial in large arrays using specialized controllers.
Audio is a piece of cake, SD video is from 3.6 to 7.7MB/s compressed and 20 to 27 MB/s uncompressed. HD compressed ranges from 3.6 to 14 MB/s. Uncompressed HD ranges from 46 to 165 MB/s.
you could get 4 of these drives... Newegg.com - Western Digital Raptor WD360ADFD 36GB 10,000 RPM 16MB Cache Serial ATA150 Hard Drive - OEM
$99.99 each and probably would get sustained rates of well over 200 MB/s, which would allow you to do uncompressed 1080i video (which no on does anyways) and 144 GB of storage (if you need more, use 150GB drives instead of 36GB).
The Mac Pro actually has 2 extra SATA connectors on the motherboard, so you could put a nice big Hitachi 750GB drive with 32MB cache in the 2nd optical drive slot (must us a right angle SATA cable as it is a tight fit). This drive would host the OS and also serve as backup for the RAID-0 volume.
If any single drive in the RAID-0 volume goes down, you loose the volume, that is why it is imperative to use the RAID-0 volume as a working / scratch drive, but archive all materials to a safe place when you can.
The Mac Pro comes with the ability to mount the drives as a software RAID volume. You may hear of hardware controllers offering superior capabilities over software, but this mainly applies when using RAID-5 or RAID-6, where parity calculations must be made. RAID-0, although MAYBE utilized better with a hardware controller, is just fine with a software solution.
It comes down to budget... $400 for 4 10K drives, plus a few hundred more for a 750GB, seems like the cheapest solution out there, using the hardware you will have, no external cases, and able to do even the most I/O intensive task that I can think of. Why over think it?