If your OS is currently on a HDD, then you should definitely go to an SSD. You'll see a 5X increase in OS and program load times going that way. Adding more SSDs into a RAID isn't a very good choice in my opinion, and has virtually no effect on gaming. Also keep in mind that SSDs are a RAID in themselves with multiple NANDs and multiple internal NANDs per physical chip. So a 250GB SSD often is already essentially the same as two 120GB's in RAID 0. Only difference is it shares a single mSATA port. Putting them into a RAID 0 is just adding in a lot more chances that it'll fail and you'll lose all data.