I've been assessing how small a file will still give a completely satisfactory exhibition-size print. The answer is - surprisingly small.
One of the images I experimented with has been posted here before ("Ten images from Japan plus ten more") and I made a 55cm (22") print from the crop as shown below. I added a few pixels in Photoshop, did some careful sharpening, and printed on my regular stock (Epson Enhanced Matt), getting a very pleasing result.
