Gaming.what is your Pc used for?
An SSD is meant to be a great addition to any PC, as conventional mechanical hard drives are (in my opinion) the main thing bottle-necking PC development these days.
This Intel X25 is therefore what I would recommend. Installing your OS onto this, as well as commonly used programs such as your internet browser, while using your SATA hard drive as your main storage for music, videos, games etc, would give your PC a dramatic increase in speed and performance.
Say if you hardcore one or two games such as for me COD4/WoW, what are the performance increases like for loading etc?