Raid 0 really will only offer faster performance if your transfering huge files, like video editing or something. In everyday use, it's a little faster than a non-Raid'ed system, but not alot. High sustained transfer rates don't mean a whole lot for destop use (including gaming like loading maps), since most of the time spent accessing data, is spent on your hard drive simply looking for and getting to the data itself. So a higher spindle speed will definetly help out more there.
And to the people saying a raptor is faster than a 15000rpm drive, why don't you go buy both and see. I just got a Seagate x15-36lp and it's quite a bit faster than my raid'ed raptors. Apps load faster, game maps load faster and my system feels a bit more responsive (though not as big of a jump as when I went from 7200rpm drives to 10000rpm drives).