" I have a ten year old ex-racehorse who is a speed 
  freak also.  He to scares me, I refuse to go to anything other than an 
  eggbutt snaffle, but I will use a running martingale for leverage.  I am 
  also looking for advice on this matter, so all you experience people, speak 
  up."
   
  Take him on a really, really long ride and let him 
  get good and tired out.  Then take him out the next day, and so 
  forth.  He'll learn.