Buy an SSD.
. 3 raptors in RAID0 gives you what? A more or less unreliable 240GB disk that performs 'ok' - for alot of money. While with a smaller SSD you have something that performs 'fantastic' and costs the same - you would lose on some space however.
Still i think its wrong to use expensive HDDs to get a high I/O performance storage setup these days - that's where SSDs are for. Use 5400rpm HDDs instead to store your bulky files - makes much more sense to me.