I have a 15" mid-range macbook pro from 2009. I have had every new OSX version since then, and I always used the 'upgrade' function(so never a clean install). To improve performance I installed an ocz vertex2 ssd 2 years back, and I replaced the superdrive with the original hdd. Now, I notice that performance has been dropping: slow boot times, iTunes always hangs when it's syncing and downloading updates etc.. Would a clean install improve anything? But can I use time machine to restore files, or will it make the whole thing slow again? Maybe I could try mavericks beta (and return if it's too buggy), because it's really since mountain lion that performance has dropped.