Yeah, I'm figuring about that too. The actual difference between Hi-Res.ver and compressed.ver isn't that siginificant. So next time, maybe I would convert them to jpg about 300kb per page before I upload them.
I download the archive, then i convert the file to jpg myself. It reduce the file from 5.19 GB to 1.90 GB. It possible to reduce the file size without sacrificing resolution. So the previous png file and current jpg file has same resolution. Only the file size reduced. Depend on image, perfile is 1-3 MB. Of course you can reduce the file size further, but it sacrifice the resolution. Myself prefer original resolution though.