Probably get best overall performance from a single Raptor, then.
You will get faster Sequential Transfer Rates from a pair in RAID 0, but the latency will be *higher* - just as Mondoman said. There is also a CPU overhead (though it's not very much, it *is* a couple of percent).
It will be faster for certain games (which just stream data off the hard drive and don't do any work with it), and for content creation or HD video it will be faster. For everything else it will be slower - and that includes most games.
Then you've got the added data insecurity, though I assume if you're going RAID 0 you'll have a proper backup solution... (hint, hint
***edited 3/11/6 - thanks Mondoman!***