If you go install 7 you'll have to take Systemd but 6 is pretty far into it's support cycle. If you you like Gnome 2 you can install Mate on 7 if you do a minimal install and add a repo. CentOS like most Linux distros is more stable than OS X if that's your thing but in order to do a lot of desktop stuff you need to add more repos. The problem with multimedia repos is you sorta have to pick one because the different ones will conflict. IMHO CentOS really isn't worth the hassle unless you work on RPM stuff at work if I were in your shoes I'd just out Debain with Mate on it and be done with it.