FFV1 has been gaining popularity as an archival (lossless) video codec. It gets about 2:1 compression. I would guess that higher-res scans would compress better because neighboring pixels would look more similar, but I haven't seen any actual data supporting that. Lossless audio codecs like FLAC also get about 2:1 compression, so I'd use that as a rule of thumb for archival audio & video in general.