It's much easier to make a mixte fit with component adjustments than it is to do the same with a traditional frame. That said, I have a mixte that is so small that it was going to look really silly with the huge stem and seatpost I needed to make it fit.

As far as I can tell, though, most mixtes came in two sizes, small and smaller. My pink Nishiki is the largest mixte frame I've run across. I'm 5'6 and in its original configuration, it was a bit too small for me.