If you find tar to be fast enough for you, then ignore me.
make a dar archive
dar -c <archive_name> -y -s <size> -R <path>
-s - size of slices
-y enable bz2 compression
Extract single file:
dar -x <archive_name> --go-into <path>
<path> is the path of the file you want to extract.
PS. If you made your archive with archive name "backup" use "backup" also as archive name in extraction and not not the spesific slices that dar has made.
Here is a link if you want more help