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Cable discs should be fine?
Maybe. Depends if the hardware can melt or if the pads are particularly susceptible to heat.
A well set up V brake is a good brake. The pads are massive and there's loads of mechanical advantage in the design, they are simple and they weigh nothing. They didn't stick around on MTBs long because unlike discs they work better when things are clean and dry and when the rim is true.
Ah, so worse as less rim-track to dissipate heat on.
Cable discs should be fine? Or are they not significantly better than V brakes - I don't think I've ever had a V brake bike