Larger ssd devices are faster.
There is no advantage to raid-0 with ssd devices or, for that matter with anything else either.
I know, I tried it.
Raid-0 has been over hyped as a performance enhancer.
Sequential benchmarks do look wonderful, but the real world does not seem to deliver the indicated performance benefits for most
desktop users. The reason is, that sequential benchmarks are coded for maximum overlapped I/O rates.
It depends on reading a stripe of data simultaneously from each raid-0 member, and that is rarely what we do.
The OS does mostly small random reads and writes, so raid-0 is of little use there.
There are some apps that will benefit. They are characterized by reading large files in a sequential overlapped manner.
Here is a study using ssd devices in raid-0.
http://www.tomshardware.com/reviews/ssd-raid-benchmark,3485.html
Spoiler... no benefit at all.
When you load windows, it will create a hidden recovery partition on any other drive available. That complicates reuse of that hard drive later, hence the recommendation to load windows with ohly the windows drive installed.