I'd go with the C'dale over the Santana because as mentioned it's a better frame. You can always upgrade components down the road as they wear out, or if they don't meet your expectations.

Also, given your single bikes, and racing background, the handling of the Santana might be a bit stodgy for you.

Not to start a flame war, but Santana's tend to handle differently, more stable, but less manueverable, for lack of a better description, than some other tandems, such as the Co-Motion you're also looking at.

That's not to diss Santana, but you may want to ride several brands to get a feel for what you like.