actually, what i did was to have a ssd in the main 2.5" bay area, and use a 1tb 5400rpm 7mm hdd for storage. Im not sure if the SSD can boot off the optical bay, if can, i would move my ssd over there and use a 9mm 2tb for storage.
if OSX and programs files are on the SSD, the speed boost is significant. a 250gb to 500gb ssd should be enough for everyday programs. I use the storage drive to store music, video, and photos.
Pro has longer longevity hence the 10 years warranty. But the price of a 250gb pro is about USD$50 more and 500gb pro about USD$100 more. Therefore I had chosen the 500gb EVO at USD$199.
real world performance difference, i read (i think storagereview.com) mentioned that evo exceed pro in some areas, cos of the SLC used in a small part of each chip.
I didn't really like the idea of fusion drive, if 1 drive fails, all data will be gone. I rather manage programs files and data files seperately on their own. Data I also use a external drive to backup.