Originally posted by gazonk +1 to that. But at least I finally finished my 2017 calendar, a few days into February
Our son printed and framed some of his favorite shots from last year as a Christmas present for my wife. I must say that even ISO 3200 shots from his K-s1 look quite good printed. That underrated little camera has a remarkably good sensor (and the AF seems more reliable than on my K-5 as well).
I print A3 calendars every year, and most images are square, which means a little over A4 full page.
As regards sharpness and colours, on matte paper calendars, images taken at 6MP with my high end compacts Fuji X10 or Fuji X-S1 look almost as good than those coming from my 24MP K3. I even had one nice full page using an image coming from an Iphone.
What APS-C brings is mainly more appealing images thanks to more subtle contrast and more subject separation (bokeh), which produces a kind of 3D effect.