When set to use BackupHistory on save...
#1: I set MaxBackupSize to 75MB
This makes saving large files *really* slow - mostly because Slick does a DIFF operation on two really big files ... diff is pretty slow.
In the case of large files, Slick could keep history as N full-copies of the files and not do any diffing.
I have plenty of disk space to burn - its cheaper than my time - so please, use the extra space!
#2: In Tools > Options > File Options > Backup, it should 2 sets of options: How to backup large files and how to backup small files.
Then, I could choose History for small files, and CreateBackupFileOnFirstSave for large files.
Also, for small files I could choose "Use VSDelta" versions, and large files I could choose "Number of full-copies to keep for backups"
If the file is too big (max size to backup) then slick doesn't do a safe-save or keep any extra copies of the large file around: https://community.slickedit.com/index.php/topic,14136.msg55516.html#msg55516
When not keeping history on a file, Slick ought to do a safe-save when possible to avoid dataloss on error during saving. (In the extremely unlikely case of out-of-disk space, prompt to user to delete the backup and continue saving).
#4: Maybe if BackupOnSave had the option to keep multiple full copies, then integrating File history and Multifile Undo would get a little easier :-)