Lead screws are pretty cool, and they don't have to be slow. An 8 start 1/2" lead screw travels 1 inch per turn.
We used some of these (
http://www.mcmaster.com/#99030a400/=sr50n0) on our climber in 2013, and they were decently fast. To travel 30 inches carrying a 150 lb robot took under 5 seconds. If we weren't carrying the weight, we could have done it faster.