Christopher,
Ok with a software RAID, you're processor is being used to not only to run your OS but also your application(s), be it FCP or something else...this is true with an internal software RAID created through disk utility generally RAID 0 or 1 or with an external solution.
Your processor should be used for 2 things ideally, 1. Running your OS & 2. Running your applications.
In order to run a software RAID, you're going to use some of the processing power of your computer, although perhaps not as much with newer machines as as the case in the past.
The other problem with software RAID is you're running your software over software, if your OS crashes, that could be a potential problem & cause your software RAID to crash. You mentioned RAID 0, again, you'd be using some system resources from the processor to run it & get speed, but a crash means you could potentially lose everything.
You've got many options for a hardware RAID 1, 2 bay FW 800 connected product, we have a product called the
SOHORAID SR2 for instance, that does an automatic RAID 1.
Any other questions, please do ask. I'm on here to play advocate to Bob, (whom I know pretty well). We're all here to help.
Jon