USAFRet :
Just use them as two drives, C and D.
Merging them in RAID increases the potential for failure and complexity, and little if anything for real world performance.
Two small reasons as to why this wont work:
You need lots of consecutive storage for video editing, photo editing, or other "scratch disk" needs
You have a lot of games that have to be stored on the same volume (e.g., Steam games) but can't fit them all on one drive
And those steam games wont update on another drive neither, and third party programs may not work.