I'm running Debian 9, and I installed Electrum 2.7.9 using the SPM.
However, the Electrum website has version 2.8.3 as the latest, should I upgrade to the newest version or
stay with the current?
yep uninstall using apt-get and then follow the instructions on the download page to install the latest using pip2:
electrum.org/#download.
next time when a new version comes out you repeat the install using pip2 and it'll update you.