Just a note on the 5S Shiftmate for anyone reading this thread: The parts are available as shown on the Jtek website (www.jtekengineering.com), but their website is undergoing an upgrade and these newer parts are not yet linked to their cart. If you need the 5S or any of the straight Shiftmates just give them a call.

On a related note I haven't completely given up on my Shimano/Shiftmate config, but I do think that the shape of the housing loop combined with the right angle shiftmate may create a bit of take-up in the cable as the cable tension increases. I've ordered a SRAM RD and 5S shiftmate and I don't doubt this will be the final configuration.