With a 60 lb robot with low speeds and low accelerations, I don't think you'd have any problems with the belts. We haven't had any problem with skipping teeth. The trick is to set the pre-load just high enough to cover the needed accelerations but no higher. That will minimize the stress on the core fibers on the outer edges of the belt. Your other option would be to use urethane belts with a kevlar core. They are more flexible and would be much less prone to failure, and the small loss of stiffness would not be a big issue for your application.