Do you plan option doesn't compress files with a certain extension?
I'm interested in this issue as well,
I'm using 7-zip command-line to make big backups of several user accounts (which makes 8 compressed files up to 100 Gb). In this accounts, users store avis, jpegs, zips, rars, etc.
Could be any option to exclude from compressing this files and storing them. The final compression time will reduce a lot while the final size of the compressed file would not increase a lot.