keep the WD, if you go RAID0 you'll want another drive to use as backup (although it might be hard to fit 3 drives in your case)
edit: or you might just get a second WD, and run them in RAID0, (like mine) on my adaptec1200a card ($55 at circuit city) i can get tranfer rates up to 85MB/s, and averages at 72!
these are great drives, and the 3 year warranty is great. (SATA might be faster, but you probly wont be able to tell the difference)
BTW, what are you planning to run on this setup? games/vid editing/os?
RAID is good or vid editing, but berware that mine doesnt do simutaneous writes! only allows one at a time.