Ahci does make a huge difference, both with SSD and with Sata/6000 Hdd. They say Seven has its own good Ahci drivers.
The Agility was not the best choice. Their older Vertex is clearly faster. Pity for you. An Ssd is difficult to chose; read a lot, compare the controllers (Indilinx, Intel, Samsung), don't rely on contiguous read and write speed.