I'd read about this upgrade on Wim Schermer's blog. Than he wrote an article in the 'Ligfiets&' together with Wilfred Quemo Quest. Today I received my set of cables.
It's like going from plastic to metal brake levers. More stopping power, more 'bite', less flex. Jagwire brake cables, highly recommended for every drum braking velonaut. At a price of €14,-, shipping within the Netherlands included, this a must have without downsides. I got mine from Velomobiel.nl
A normal brake cable is built up like a curling telephone wire. A shift cable is stiff, but could split open when used as a brake cable. I just was lucky when I used index cable on the brakes of my Alleweder. Jagwire combines the curly wire that doesn't split with the straight cables that don't flex. The result could be that your stopping distance at 35kph goes down from 8 to 7 metres. I don't know what my brakes performed like before the upgrade, but it sure feels a lot better now. From 36-0 costs less than 7 metres, possibly even just over 6. A fast velomobile needs stopping power too.