If you have an Intel based mobo (X58 or P55), then yes on ACHI to get the most out of the SSD.
How'd it go, noticed this post is 3 days old. Did it go okay?
But, you have to do it before installing the OS. Actually, there is a registry tweak, but I don't know what it is. If you change the SATA setting to ACHI from IDE after OS install, you have to re-install the OS.