Activator or Superboat are going to be the fastest. Low seventys in not too much to expect form a large single with at around 500 horse. It depends of what you are looking for and how much $ you want to spend, there are alot of nice boats that you could look at. Do a search there are alot of threads on this topic, the bottom line is how much cash you want to spend.
28 Active Thunder
28 Nordic ( I have owned one)
28 Checkmate ( I have owned one)