Sheldon Brown's article on cantilever says that "bottoming out" comes from too much mechanical advantage.
"If you have too much mechanical advantage the lever will be all-too-easy to pull, but it will run out of travel and bump up against the handlebar before the brake is fully applied. Once the lever hits the handlebar, it doesn't matter how much harder you squeeze! If you try to correct this by tightening up the cable, you will wind up with the brake shoes too close to the rim when at rest, which will cause them to rub, especially if the wheel isn't perfectly true. "
http://www.sheldonbrown.com/canti-trad.html
I switched from the Oryx's to the CR 720 and am happy.