Slideshow - which is better?

[Comatose]

For a slideshow with no transitions, would it be better (compression wise) to use VFR to make each picture last as long as it needs to, but have no dupe frames, which would allow for a very higher bitrate...

-or-

Do it the "normal" way - dupe frames to make each picture last as long as it needs to and use a lower bitrate? (the dupe frames are all, of course, real, mathematically equivalent dupes - no noise)

Which would, in theory, provide a higher compression ratio (quality:filesize)?

[cacepi]

Which would, in theory, provide a higher compression ratio (quality:filesize)?
If the dupes are truly dupes - no noise - then their blocks should be skipped if they're encoded as b-frames. The bitrate penalty for encoding as CFR would probably be negligible. You could encode at 12fps with 16 b-frames and be done with it before messing around with VFR.