I'll chime in on the side of those who find the Tektro 556/559 calipers stop well (Koolstop pads, Shimano R400 brake levers). I've had my Bleriot with 556 calipers on tours in the mountains several times, and not had any problems with inadequate stopping power. The braking isn't as good as with disc brakes (in over 50 years of cycling, I've never used a rim brake of which I would say that), but it's very little different in power from that with cantilevers/centrepull/v-brakes that offer similar tyre clearance.
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