Mac image viewers or editors that can handle files larger than 30,000 × 30,000 pixels

The GIMP will load such files and allows such large images to be created though you'll need huge amounts of memory to get things done within a sensible timeframe - unsurprisingly, it seems most 'everyday' packages are not optimised for images of such enormous dimensions.

Creating a 40,000 x 26,667 pixel test image by resizing a smaller source picture took a long time; it didn't help that the resizing algorithm ran on just one CPU core. I gave up my first attempt with the default interpolation settings and re-tried with no interpolation in order to create the test image. This second attempt took a few minutes from starting, to finishing, redrawing, settling down and allowing user interaction (not paging in/out - it just sat there "thinking" for ages after apparently having finished the resize and updated its image view, but not allowing any interaction).

http://www.gimp.org/macintosh/

I saved the file as an 8-bit TIFF (GIMP still doesn't support images deeper than 8 bits per channel...). This loaded into OS X's Preview.app surprisingly quickly, even though Preview refuses to create images > 30,000 pixels wide or high. Trying to do any edits, however, took so long that I gave up and force quit Preview.

The Finder even showed a thumbnail preview of the file after a while.

More success with Aperture - it took a minute or two to import the test image but thereafter was startlingly fast when performing modifications. The auto-fix preset and similar took just a second or two to complete. It took much longer for the package to fill in things like the histogram under the 'Metadata' tab but it didn't stop the sliders being used to adjust the image.

Exporting at 100% was glacially slow. You'd want to process any images, then set up all your exports before going to bed! At least it does them in the background so you can carry on working while export tasks are being processed. Aperture costs a reasonable chunk of money, but at least it can be found on the Mac App Store for considerably less than a boxed copy - $80 in the US:

http://itunes.apple.com/us/app/aperture/id408981426

Note that SilkyPix (if you're familiar with it) in the version I have only allows export sizes up to 10,000 pixels wide or high and refused to load the 40,000 pixel wide test image. Sigma Photo Pro 5.0 also refused to load the file.