The slideshows use the cropped images to make the effects more consistent. The blinds one works only with the cropped version. If you used the dissolve one though, you can change it to use the proportional images. On line 14 in the galleries/slideshow_dissolve/index.php file, changing 782c to 782p would change it.
The dissolve one also has controls for the slideshow. The blinds and wide galleries are more designed to be unattended slideshows.
However, check out this sweet piece of documentation on how to further customize the slideshows: custom_slideshows.php