In my opinion, you should buy a 250gb ssd instead. I have a 120gb ssd as my boot drive and it's always at least 80% full. You have to constantly be vigilant about it not letting it get too full or else performance will suffer. It's super annoying. I bought another 120gb ssd drive (so now I have two 120gb ssds) thinking it would alleviate my problems but it didn't solve it at all, since Windows only uses 1 ssd to store all the OS files. I wish I would've just bought a 250gb one from the start.
EDIT: If you decide to go with 120gb ssd then download this program and make a shortcut on your desktop. You'll be using it fairly regularly. Helps you quickly find folders/files that are hogging up space.