The main thing an external drive brings to the party is concurrent reading & writing with the internal drives, which gives you a minor boost in speed, and a lot less work for the internal drives. A FW 800 drive would be just fine, and a FW 400 would not be bad, either. But that RAID? You'll have the advantages of a good deal more storage, not any extra speed to speak of.
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
[Andrew Riss]"Or does AFX rely mostly on the processor and RAM?"
Totally depends on your project and workflow. For most people working with little footage and lots of effects, AE is bound by the processor and RAM, and the speed of the disk has little impact.
However, if you're working with many multiple footage items in a single comp, or if you like to pre-render or proxy to image sequences to speed up your workflow, your project could quickly become disk-bound. If that's the case, the RAID could speed things up.
I recommend a monitoring tool like MenuMeters [link] to let you see how your system is performing during a render. You could also just watch Activity Monitor on a Mac or Task Manager on Windows. If you see a lot of disk activity but not a lot of memory or CPU activity, then your render is probably disk-bound.
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events