Previewing A3 quality

That would depend (a) what resolution you were printing at, (b) whether you were matching the long side of the image to the long side of the paper or matching the short side - A3 is squarer than what comes from the camera and (c) how you were scaling it - with most scaling algorithms an image doesn't become progrssively blurrier but passes through certain particularly sharp sweet-spots.

In case that's not convinced you that's it's not a good measure, plugging some numbers in to get a rough estimate gives us this: the long side of A3 is 16.5" (assuming full bleed) which, at 240 ppi is 3960 pixels. The long size of a full resultion photo from the K-5 is 4928 pixels so to fit it to an A3 print you would need to reduce the image to 3960/4928=80% of its original size.

Cheers,
Paul

The image at 300ppi is roughly A3. Change the ppi but do not resample the image. But to get the image to roughly A3 size on screen, zoom to a 33% view. There's no substitute for a test print though! The appearance of noise and sharpness will look different on a print (better).