This is a very informative post. If you could post pics of the rear triangles of these, it would make it even more so.From experience, the 160mm style caliper perch, chainstay mounted is best in many ways. There is less weight, there is less lateral flex, chainstays are stronger than a dropout. All except the less weight make the brakes work better.
As for the cable run, if the bike does have an acceptable route, such as a diagonal frame tube, the alignment is pretty much perfect with the shortest cable route possible.
As evidence to compare, we have experience with three tandems with disc brakes. A Fandango 29 off-road tandem, a Ventana 26 full suspension off-road tandem andour Co-Motion Roadster with front and rear disc brakes.
The Co-Motion stops very well, but has obvious frame flex and torquing of the LS dropout. Not that I have seriously tried, but on dry pavement I am not convinced the Co-motion can skid the rear tire. It may but might be enough stress to damage the dropout with the leverage provided by the perch and radius of the brake. The caliper is mounted similar to the Calfee and is without any bracing.
The Ventana also stops well, it also has visible chainstay and dropout flex. There is no means to flex the seatstay or entire frame since the brake caliper is dropout mounted on the lower suspension arm (swingarm). This bike sees very heavy braking in all forms of terrain, some low grip other times high grip. It is not uncommon to be on the brakes so hard to have them lock up or induce brake chatter in hacked entries to corners.
The best tandem disc brakes on a tandem we have owned that were cable operated were on the Fandango. Alex did a very good job of placing the caliper on the LS chainstay. The mounting perch is based on a 160 series mount but designed for a 203 rotor. Once installed, this brake is rock solid in feel and can easily skid the big 2.35 rear tire on asphalt.
In this teams experience it does make a difference.