RE: OS 91 or Evo 1.00 for Little Toni?
Unless you are all-out going racing with someone, Id probably give the Evo 100 a try.
Put a 13x6 or 12x9 prop on it and it should turn up around 12,000 rpm
Muffler install and selection is the tricky part with the Toni. The Evo has the same 42mm bolt spacing as the OS, so you can used the same muffler options with either the OS or Evo.