Putting the two smaller drives in RAID 0 would give you about twice the bandwidth of each small drive. Some say RAID 0 doubles the chance of failure, but I'm not sure that applies to SSDs - a Vertex 4 256GB would probably use the same type and total number of Flash chips as 2 Vertex 4 128GB drives in RAID 0, giving the same overall chance of failure. RAID does add some complications, as Windows install might require the RAID driver from a usb memory stick, the RAID controller pauses to give you a chance to enter setup (slowing down system startup), and you'll want to make sure your RAID controller supports TRIM.
A failure in a RAID 0 would render the whole array inoperable, but might only require replacing one drive (as long as an identical drive is available) to create a new array, then you'd restore from a disk image (or reinstall windows if you only back up personal files). How were you planning to use two drives then?
Okay, I looked up specifications for the Vertex 4 128GB and 256GB models. They have identical weights and MTBF values, so I was probably wrong about the two smaller drives having the same type and total number of Flash chips as the larger drive (two drives in RAID 0 still wouldn't have exactly double the chance of failure, but close enough). The 128GB drive has a slightly lower sustained sequential write in the specs, but other than that, performance should be about the same.