Lightbox-style gallery with download link

I’ve spent many hours trying plugins and searching the forums, but haven’t been able to find what I’m looking for. I’m looking for a lightbox-style image gallery with the following two options available:

1. Ability to show an image other than the original inside the lightbox (i.e. medium or large). I know there are plugins that resize the originals to fit the current window, but I don’t want to waste the bandwidth loading the original images.

2. Have an automatically-generated download link for the original image in the caption.

Am I the only person in WordPress history who’s wanted to do this? Thanks for any help you can provide!