There is generally no real world(vs. synthetic transfer rate benchmarks) performance advantage to raid of any kind.
Go to www.storagereview.com at this link: http://faq.storagereview.com/tiki-index.php?page=SingleDriveVsRaid0
There are some specific applications that will benefit, but
gaming is not one of them. Even if you have an application which reads one input file sequentially, and writes
it out, you will perform about as well by putting the input on one drive, and the output on the other.
If you can't get a ssd or velociraptor, then I would suggest "short stroking" with a 640gb or larger drive. That is deliberately using only 10% of the large drive's capacity. That puts all your data on the outer 10% of the drive where transfer rates are higher. Seek time is also less because the access arm needs to only traverse a small part of the drive. Short stroking is why you see such impressive boot times in reviews of terabyte sized drives.