By far the best photo editing program is Live Picture 2.6.2 created by a team of French software engineers who were also artists. It was produced by John Sculley's Company Live Picture and originally sold for the equivalent of $5,000+. I use it for almost all my creative photography. I can do things with it that Photoshop or CS would choke on. And it only runs under 8.1 - 9.2.2 or under Classic (Tiger machine.) I have posted pictures at waeshael.leicaimages.com
And I have written about photography and this software at waeshael.com
If you are interested in learning about this program, I can provide the software which is no longer being sold or supported, and I don't think anyone will mind if I make a few copies. You can edit files 100+ megabytes on an old Powerbook with 128MB of memory, so handling modern TIFF images of 60 - 100 MB is no problem, and you can do an unlimited number of layered images. All images have to be converted to TIFF and then to IVUE format and there is a stand alone app to convert to IVUE. Everything is very fast. The program loads in 5 seconds. It is quite brilliant, and a joy to use compared with PS. Older PS 3.0 - 5.0 could save JPEGS as IVUE files by exporting to IVUE using a plug-in provided with Live Picture. And the LP image can be exported to PS for work with filters and the filtered file drops back into the composite in LP.
If any of this makes any sense to you, then have a look at LP - ask me anything you want. I have been using it since 2000. Several world famous photographs used it exclusively until Intel ruined the Mac and made it Mac for dummies (but I do use SNow Leopard as my main work station and I have three Macs running El Capitan - which are almost as fast as my Pismo running 9.1)
Cheers