If you put two SSDs in a RAID-0 array, it will be faster than one larger drive. However, if one drive fails for whatever reason, all of the data is lost. You also lose automatic garbage collection when SSDs are in RAID.
You won't see any huge differences. It will be noticeable, but only a few seconds here or there when loading game levels.
I recommend getting a single drive -- in particular, one of these: Crucial M4 128GB, Plextor PX-M2 128GB, or Samsung 470 128GB. That will hold Windows and a few of your most-used programs. Then get a 1TB or 2TB hard drive for the rest of your programs and data. Make sure you do research on SSD optimizations and what steps you need to take to keep your SSD from filling up.