RainSong's OM-1000 and CA Guitars 5S-CE are similar guitars. Certainly – carbon fiber construction, small, slim bodies. However, when placed side by side, the two are quite different instruments.
Let's start with sound. The RainSong reminds me of a guitar with maple back and sides; Indeed, RainSong's website describes the OM-1000 as having a "crystal bell clarity, balance, superb separation of individual notes." This is a great guitar for individual note-picking, but strumming does not work out well. The CA 5S-CE, on the other hand, has a very "woody" sound that reminds me of a guitar with mahogany back and sides. It's also got a deep voice, and, like its cousin the Cargo, will surprise you with the bass and volume coming from such a small-bodied guitar. This guitar is also built for individual notes, as is the RainSong.
Next, let's look at some structural differences. Both guitars have slim bodies, but the RainSong, at 4.125 inches, is worse than the CA is, which is at 3.25 inches. Also, the CA has a bevel on the top of the back, which allows for the instrument to fit snugly against the player's body. Also, the cutaway is quite different. The RainSong has a soft cutaway, but because of the heel block, you need to make a small hand shift to get beyond the 15th fret. The 5S-CE has a sharp cutaway, and because of CA's double cutaway – back and sides – your hand slides smoothly all the way up to the 20th fret.
Some other noticeable differences: Both guitars are equipped with Gotoh tuners, but the RainSong's have 1:18 ratio, whereas the CA 5S-CE [http://www.macnichol.com/mm5/merchant.mvc?Screen=PROD&Store_Code= MGAM & Product_Code = 5S-CE & Category_Code = CA_Guitars] have a 1:15 ratio. The RainSong has a glossy natural finish that highlights the carbon fiber weave, whereas the CA is available in either carbon reveal, red, wine, or charcoal. The RainSong's electronics are LR Baggs On-Board System, where the CA comes with the Fishman Acoustic Matrix VT. Also, the RainSong comes with a hardshell case, whereas the CA 5S-CE comes with a heavily padded gig bag.