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You're comparing the SATA3 Marvell 9128 (PCIe 2.0 x1) 500MB/s max vs Intel SATA2 (full bandwidth) 2*300MB/s = 600MB/s max. In RAID 0 the edge goes to Intel SATA2 ports on RAID 0. Conversely, with a single SSD on the Marvell 9128 you'll see 370MB/s~390MB/s.
Your choices for the most bandwidth: 1. Intel SATA2 ports, 2. New X58 with Marvell 9182 (no typo) (PCIe 2.0 x2 lanes) 1000MB/s max, or 3. LSI x4 or x8 PCIe SATA3 Dedicated RAID Card which costs more than the replacing the MOBO.
Gigabyte G1 Series and GA-X58A-OC offer the SATA3 Marvell 9182 chipset; see - http://www.gigabyte.us/products/list.aspx?s=42&jid=1&p=2&v=1