Unlimited FPS fix breaks the game: http://community.pcgamingwiki.com/topic/1805-i-was-useful-today/#entry8060 I think it should be removed from the article.
Topic on Talk:The Godfather: The Game
Potentially applies to 60 FPS fix as well.
It doesn't. Tried it myself.
As for the game speed increase. It'd be nice if you could record that and put it as reference so there is 100% undeniable proof and people won't question it.