I wouldn't recommend putting the SSDs in a RAID configuration -- for one, as Satcomer said, they're different sizes, and for two, they're from different manufacturers.
You typically want all your drives in a RAID configuration (other than a JBOD RAID) to be identical in size, from the same manufacturer, same drive model, and from the same manufacturing lot (at least all of these are true for spinning-platter drives).
The SSDs on their own are going to be mucho fast -- I don't see any reason to put them in a RAID.
I would recommend putting your OS X installation on the 96GB drive, since it's using a native SATA port. The 64GB drive in the optical bay may be on a slower SATA bus -- I'm not too familiar with the newest Mac Pros, so I don't know this for sure, but historically, optical drives were placed on a slower bus because their transfer speeds were much slower than hard drives. This may or may not still be true of the Mac Pros, especially the one you're using.
