On the many sites I tend to read on the topic of photography, one of the things that becomes clear is that gallery prints are often done somwehere between 240 and 300ppi, with 300 being the desired end, which is why many art photographers lean towards medium format, the image sizes lend themselves better to such print resolution and very large outcomes.

However, smaller formats can produce stunning prints, but the key to that is viewing distance. One of my friends, recently, got a pretty good look at a billboard close up and was surprised at how "bad" it looked from that view. I wouldn't be surprised, the image is intended to be viewed from hundreds of feet away and printed accordingly, and that's the point. If you scale up an image to print on a larger medium that exceeds the 240 to 300 figure I mentioned, then the viewing distance has to grow with it. Hard to do in a gallery, but not impossible, and software is getting better with this as it progresses.