check out this cool tool. You can use some of those unused RAM for cache to improve hdd Performance
[video=youtube;mP42SmFzR3M]http://www.youtube.com/watch?v=mP42SmFzR3M[/video]
http://www.romexsoftware.com/en-us/fancy-cache/
[video=youtube;mP42SmFzR3M]http://www.youtube.com/watch?v=mP42SmFzR3M[/video]
http://www.romexsoftware.com/en-us/fancy-cache/