His Greinke and Butler for my Kershaw and Votto?

I wouldn't do it. Greinke has had just one good season and keep in mind, he still plays on a crap team, which really limits the number of wins he's gonna have. Kershaw meanwhile is on a contender and could end up with more wins than Greinke and an ERA near Greinke's. Also, Butler is a really hot and cold player, personally I think he's a sizable downgrade from Votto. I'd stick with what you have now. If you can, try to get Lince if at all possible, or Hernandez, Halladay, or Sabathia.