You will have a substancial increase in performance in anything that relates to the system (boot time, calling programs, etc.). Moving the user data off the SSD and to a HDD is the standard procedure. That way you can get away with a 60GB SSD or even a 30 to 40GB SSD. The Windows 7 should not take more than 20GBs including a good selection of programs - Games though may take more space. Suggest you check the size of your current OS installation ( e.g. with WinDirStat
) so that you have an idea what your specific requirements are.