In spite of the fact that you did not mention what apps you want to use, I am guessing that raid will probably help you out more. (assuming that you are going to be using raid to double/triple output as opposed to just using it for fault tolerance). Loading apps, especially windows will be dramatically faster. Most processors these days are overkill for even gamers and graphic artists (I mean come on now, how many frames/sec do we really need... TV is only displayed in 30). However, there are few times when I have said that my hard drive is overkill. So my personal opinion is that RAID is better than dual processing.
-k
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