RAID0 won't do you much good for blocking I/O in games; only one HDD can be used at a time in many cases; called a queue depth of 1.
For gaming, the only solution that's vastly superior in performance, is an SSD. You can use RAID0 to combine several SSDs in a larger virtual disk, but if your budget does not allow this, i would focus on separating system + gaming + data disks instead.
For gaming, using a Velociraptor may be faster than two 7200rpm disks in RAID0. But if you have the choice between these two, i'd opt for the 500GB platter one. Cache size is not that much important.