SATA3 port on motherboard and SATA-3 SSD then 6GB/s
SATA3 port on motherboard and SATA-2 SSD then 3GB/s
SATA2 port on motherboard and SATA-3 SSD then 3GB/s, but your shouldn't see any noticeable difference to a SATA-3 port, unless you use a high end SSD.