the single most important performance factor is the choice of hard disc system-

SCSI performs the best - and also with scsi there is a great deal of difference between individual drives, drive speeds, and drive capacities.
The fastest drives i tested are the Fujitsu MAU 3147 - 15rpm discs - which will give you 7-8 layers dv.
cheetah 10k7 drives around 6 layers
The slowest drives are the atlas 10k rpm drives - that HES shipped with most of their servers.

The next best single non-scsi discs are Western Digital 10000rpm SATA raptor drives.

Firewire 800 RAID systems DO NOT work that great because they use slow and cheap 7200rpm discs- these are designed for storage capacity - not playing back lots of layers at the same time.

The headline rate of the Firewire 800 RAID is not important. Firewire 800 will not work unless it uses fast drives.

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The answer is - if you want lots of layers - you have to get a proper disc system. speed of processor is not the most important factor.
Firewire 800 is not good enough most of the time.

If you want to do this on the cheap - ditch anything to do with firewire 800 - and get a single 10000rpm 150gb raptor.

Aside from that - there is no performance change between v3 and v4 catalyst.
And almost no performance change between MacOSX 10.3.x and MacOSX 10.4.x