The thing to keep in mind with SSD's is that each nand can be written on only X times, the less free space you have, the faster drive dies.
That in mind, I give 120GB SSD disk that is about 60 to 70GB full, like 7 to 8 years of life as main boot/OS drive. (based on my own 120GB ssd and it's usage in last 1.8years)
IF it has less data on it, the longer it lives.