The easy way to answer that is to look at how large you print. I have a 44" wide printer, and my D700 (on the short axis) can't print 44" @ 300dpi. I made this chat to evaluate my options. It included a non-existent model - the Nikon D4-32 - which I define as a model with double the pixels of the D7000 sensor.
For each camera, I used the number of pixels on the short axis, and divided that by various print dots per inch (DPI). That number is the length of a print on the short axis. The chart's vertical axis is the DPI and the horizontal axis is the width of the roll of paper.
This chart shows me three things:
1. what DPI I'd get for a given paper width
2. what paper width I'd have for a given DPI
3. what camera I'd need if I want to print at a certain DPI for a given paper size
How to use this chart:
How big can I print? Pick the DPI and see where it intersects each camera's line.
What DPI can I print? Pick the paper size and see where it intersect's the camera's line.
Which camera do I need? Pick the paper size and the desired DPI. You want a camera above that intersection.
If you look at the intersection of 150 dpi and 24" paper, you see D3x, 5DmkII are good choices. The D3 (thus D700) falls short of this point, and owners of 24" wide printers have a real interest here.
Now look at the intersection of 150 dpi and 36". The Pentax 645D is parked right on that mark. Very smart of Pentax. My imaginary D4-32 is a little shy of the mark, but with 2" margins all around, it is a good match.
At 300 dpi, only the medium format cameras and the D4-32 have enough pixels to print 16".
If you have a consumer printer that takes Letter size paper, any of these cameras will be fine. A 13" wide consumer printer starts to hit the limit of the D700 at 300 dpi, but all these cameras are fine. But professional 17", 24" and 44" printers are large enough that you are forced to reduce resolution below 300dpi unless you have a medium format camera.
Yes, I'm ignoring the "quality" of the pixel, upsizing and viewing distance considerations. This is just a simple chart to provide a graphic view of how our cameras compare to medium format camera.
I usually start with the print size, then decide if I can use my D700, rent a D3x, or rent a Phase One 60MP.
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Ken Elliott
Equipment in profile.