Help me, Dr. Internet!

I can't really get a straight answer on this, and am hoping someone out there has a good solution.

Every year, I make a huge several-terrabyte backup of my entire system. When I was on Windows, I used RAR for this. Good compression, was able to break it up in 4GB file blocks to make file access easy if I needed something off the backup or repair an archive.

I've long since moved to TAR.XZ for intermediate backups, but the access takes forever cause it's a single archive, so I've never used it for my large once-a-year-complete-backup.

That said, the question: would it be worth doing the Full Everything Backup with tar.xg over jumping into Windows to WinRAR it (Day 9023849283468923 of my 30 day trial!)? In general does RAR pack tighter than TAR.XZ? Can TAR.XZ break itself into chunks for easier access?

My update is scheduled for January 1st. Any help would be appreciated! And thanks in advance!

@dolari If you want to retain random access of files in the archive, avoid tar. tar produces an uncompressed archive of everything passed into it, and it's format is very sequential. If given a compression argument, then as a convenience, it'll compress the archive once it's built. Hence the dot-tar-dot-xz extension; if you un-xz that file, you'll get a single file (the tar file) as a result.

I seem to recall that there's an implementation of RAR for Linux/BSD platforms; can you use that to retain your desired accessibility?