Interaction between --log-file, --progress, and --stats

Yes.

Progress and stats printing use the same mechanism, that's why you can only have one at a time at the moment.

I think I'd prefer a flag like --log-stats-interval which if set would log stats to the log file at the given interval regardless of the other settings. Maybe at a log level to ensure that the stats were always present.

It also seems like it is getting quite complicated!