The Witcher 2 is a wrapped windows version, it runs terribly for everyone except the select few who have a 16GHz Intel i77 from 2043. Follow the threads on github and the community hub of the game.
I can't speak about the other game as I know nothing about it.
Good news: They're rewriting the wrapper for The Witcher 2, so it will be partially fixed in the future (this is why it is worth it keeping your eyes on those threads). There is already a beta channel for the game, though it doesn't yet have performance related fixes.