Not knowing your MB and which drives are on which controller - My comments are more general.
1) If your 120 gig SSD is on the same controller, unless intel chipset you will have decreased performance most likely. The controller for your SSD should normally be msahci (if intel chipset iaSTor).
2) SRT performance, when a seperate OS + Program SSD is used, is largely a hit and miss and is Highly dependent on the individual user. If you repeditively use the same files, then good performance. However; if you are reading/writing to different files alot then the performance can be simular to HDD without SRT.
3) Just a comment, I'm not a lover of Raid1 using internal drives. It really only protects against a single drive failure. Malware, viruses, MB failures, and even a PSU failure can wipe out both drives. My Past experience with drives has been positive, very few drive failures although some of the newer higher density drives seem to have higher failure rates. I always use an external drive to back up my data drives.
PS. You can use AS SSD to verify your OS + Program drive is set up properly. Do Not need to run the benchmark to check status. Open it an look at upper left. Will show you:
.. SSD make/model and firmware version.
.. Driver is msahci, iaSTor (recommended for intel chipsets), ..., if pcide will also show "BAD"
.. Partition alignment (aligned = good, not aligned - bad)
What I've done on all 3 of my systems is to to use two SSDs, one for OS +Programs and one for a work/scratch (data) disk. I place files that I know I use most frequently on the SSD as oppossed to a cache algorthum performing a educated quess. The two desktops have one/two HDD, the laptop only has two HDD bays. anf then I have 4 external HDD that can be shared between systems.