I use fairly basic shimano cantilevers and don't have a problem with stopping power- the limiting factor is my low-end brake levers. The key is in the set up- if done properly, they have just as much power as v-brakes, if done wrong they can be useless. A proper yoke and transverse cable really helps in getting the adjustment right. You should be able to set them up to either skid the front wheel or endo the bike, which is as much braking power as you'll need- any more is redundant.