I see what you're saying, but in a RAID 1, during reads, whichever device retrieves the data first will immediately begin doing so, then when the other one catches up, data will stream from both devices. That's why RAID 1 is supposed to be be as fast as RAID 0 on reads, right? Possibly controller dependent? I thought performance on would be limited to the slowest device only on writes.
Say you have lots of small files that need to be loaded and they're scattered over the 'disk', such as when booting or starting most programs. That will be fast because of the SSD low access times, even though the Raptor may never catch up under that scenario. Once you load a 'big' file, the Raptor will catch up, and it's high transfer rate will be added to the SSD's transfer rate.
Remember we're only talking about reads here.
How about 2 SSD's RAID 0, in RAID 1 with a Raptor to boost writes?
Hope my ramblings makes sense. I just really wish I could try it.