its not the speed, its the word that gets you higher damage and points. you need to keep a steady eye on the boiler, and try to use as many of the letters as possible. near the start of a level, try to expand the boiler to at least level 5 or so. then, just go crazy with words.
 "Defend your Honor!"){kind=icon}
 "Enigmata"){kind=icon}
 "Super Crazy Guitar Maniac Deluxe 3"){kind=icon}
 "Cell Warfare"){kind=icon}
 "GeoSketch"){kind=icon}
 "Dinowaurs"){kind=icon}
 "Generic Defense Game"){kind=icon}
 "Tower of Greed"){kind=icon}
 "Ultimate Assassin 2"){kind=icon}
 "Elona Shooter"){kind=icon}
 "Battalion: Nemesis"){kind=icon}
 "Full Moon"){kind=icon}
 "Frontier"){kind=icon}
 "Clockwords: Prelude"){kind=icon}