Personally, I'd still go with a 120GB SSD and a new 1TB drive for the same price as the 240GB SSD. Why? Because of two reasons :
1) My personal ways of segregating partitions. OS with ONLY OS stuff and things I want restored with the OS, like browser, e-mail client, backup program, etc., and if on an SSD, things that don't get written to every time the computer is used if possible (they go on another drive partition). 90GB's or more is sufficient in most cases for this. Now at least 2 data drives, and on two physical drives if possible. First one for data, you can cut it up into partitions if you wish. One for data you want to backup and the other for 'scratch' stuff, like downloads and temporary stuff you might put on your computer, or stuff you really don't care about losing. Last drive for backup storage so you can have more than one to return too if you need to do a restore of any drive letter.
2) Old drives have lost some life. Failure is sooner than later. Any drive past 4 years in my experience is possible to fail soon. Also, older drives are probably NOT SATA III. Your new system does support that, why not get the last ounce of speed out of it. There is little to no cost in getting a smaller SSD and a 1TB vs. a single larger SSD.