You can short stroke a single disk WITHOUT having to raid it as you wish. Use the manufacturers diagnostic disk (Seatools for Seagate, Western Digital Data Lifeguard Diagnostic for WD drives) to reduce the number of sectors to a fraction of what they would normally be (normally 10%).
Contrary to what others may say, you might get close to the same performance by partitioning off the disk, but i doubt it. Why? Because the other partition, the second it is used, is slowing down your OS partition. The heads on the disk can only be in one place at one time. So if your antivirus runs, indexing, ANY hard disk access on the second partition... the benefit of your OS/games/whatever being on a separate partition are GONE.
Short stroking will improve performance, because not only will you keep the all the data on one smaller partition/disk than the rest, but the heads of the disk don't have to move nearly as much. THIS is the reason for short stroking, reducing the capacity of the hard drive in order to improve performance.