If you want a powerful actuator that's going to lift something quickly you could take a look at the Duff Norton ones, we have two one for sale in the 'For Sale' thread

viewtopic.php?p=132782#p132782

As used in Force X, also curiously the first robot to use (and 'discover') the 35w Bosch Motors - if only I was on commision, the originals in Force X are still going strong (albeit with a brass gear to replace the naff plastic one that will fail)