If you're on Debian, an want to try and run testing/unstable, you probably want to install "apt-listbugs" -- which will warn you about open bugs in software you're installing/updating. Another option is to run Debian stable, and have testing and/or unstable chroot, managed via schroot: https://wiki.debian.org/Schroot (that page and the manpages could use an update, but having a scroot backed by lvm, and set up to mount /home works well enough for running x11 apps (the MIT auth cookie is in $HOME)).

I would recommend trying to keep things separate like that (or via something like docker/kvm/vagrant/etc) -- rather than trying to mix'n'match. You'll likely be the only one trying a particular combination of versions, and it's unlikely to be much fun.