I can't tell any difference in quality between the 470KB lossless PNG and the 150KB highest-quality JPG, so that's good, and if you can host that many shots without any bandwidth problems that's even better.

I have had an idea for something I would like to try; instead of putting all the images in a vertical line on a page, to display just one image and use an HTML form with radio buttons and a Javascript function to switch the image. Also it might aid direct comparison if all the cropped images are resized to their natural aspect ratio (i.e. NTSC 4:3 stretch vertically by 112.5%, 16:9 squash to 84.4%, PAL 4:3 squash to 93.75% etc.) and preloaded so that the change takes place instantly.

Perhaps also for selected shots that contain high detail, an enlarged area of the main image would help to show the differences between each version?