Well the Hasselblad cameras has like 24mpx i think.
(i don't know, just a pure guess..)
You can stick a PhaseOne back and get approx. 39+ megapixels...
Or stick a PhaseOne back on a Mamiya RZ67.
These sensors are ideal for billboard and posters. You'd be pretty, (excuse me), weird, if you take a "digital" medium format to a wedding or something.
They are used in portraits the majority of the time. Even professional portrait photographers today (celebrities etc') use Medium Format Mamiyas or Hasselblads etc' for their studio portraits. Regardless of how big they print. The sharpness and quality stands out...