Hi, what are you planning on running from the drive?
Keep in mind things like photo editing effects and video fx are rendered in ram, so where the difference in speed between the 2 drives would be noticeable is in using a program that needs to pull a lot of info from a drive at one time. In my case, I use audio software that plays a lot of audio tracks at once. With a Sata drive some of thee are loaded into ram and played from there, but with a SSD it doesn't need to be loaded into ram so it can all be played straight from the hard drive.
If you aren't using programs that need to pull alot of data off the drive in realtime then I would go for the slower bigger drive. In using normal system type stuff I don't think the difference between the 2 SSD's will frustrate you, but running out of space quickly will.
What are the difference in read/write times and what sort of stuff are you using the computer for?