I have a RAID 0 set up on my mid-2012 MBP. To get a noticeable performance increase, there needs to be a sustained task where the processor can process data for read/write to the SSD faster than the non-RAID equivalent. Or you need a file copy operation on the same logical drive. It turns out that my DVR app does pure file copy operations for a couple of tasks and one cannot specify a different output location. So for me, for this particular purpose, the RAID 0 is very useful when I need to edit large video files. On the other hand, I setup a database app where I have monthly processing where I need to execute some tasks that take several minutes to a hour. The RAID did not really help in that case.
SSD's with multiple NAND chips will often interleave data operations between the NAND chips and this will result in better performance. So, for specific models at specific SSD sizes, one may get better performance by buying the larger capacity SSD rather than two smaller capacity SSD's running RAID. One would have to do research on the specific SSD and specific sizes and both random and sequential benchmark data to see what the difference would be.
