In that case I would pick up one Samsung F3 1TB drive for the OS, and two Samsung F4 2TB dries for the RAID setup. At $65 and $80 respectively, $225 gets you double the storage.
You can never go wrong with more hdd space. What is your opinion on Sata III vs SATA II? I can look up all I want about the differences, but as far as experience, I have no idea if the benefits are worth it.