I can give you generic principles since you don't mention the lens of the Pentax.
Bigger lenses with corresponding longer focal (for a given field of view) are easier to manufacture, they may also have less distorsions an aberrations.
Bigger sensor elements on the sensor chip (5.3 micron for Pentax, 4.1 micron for Canon) mean simpler microlenses, and also less blur: consider that the "diffraction spot" (related to the smallest details that you can actually resolve) is about as big as the aperture value. If you have 4 microns, you need to shoot with f/3.5 or lower to record single-pixel fine details (extremely contrasty details like white on black are easier to resolve, I don't mean those).
On the Pentax you can shoot almost one stop higher and retain maximum details, meaning that you can use your lens with an aperture that more easily produce sharper images (ok, the Otus is always sharp, that is an exception).
And keep in mind that at high ISO the Canon should be better than the Pentax, medium format has always had poor noise values at more than 800 ISO.