Speed will be limited to what the sata ports can handle since it seems an older system,this has nothing to do at what the sata controller is set.Well not entirely true,at ahci will the ssd work at it's max possibilities,but it's more likely in an old system like this that the sata ports are a bottleneck.
See if there's a bios update that will add ahci and upgrade drivers.From what i know does raid (at least newer versions) have ahci options in it,but don't create an array! You don't want the ssd and hdd in one array.