Don't bother with SATA III.
It's really meant for SSD, because SSD come close to reaching the bandwidth of SATA II.
No hard disk drive will saturate the bandwidth of SATA II. My 2 x 500GB Seagate 7200.11 drives in RAID 0 only benchmark at a peak of 150MBps, half of the SATA II rating of 3.0Gbps (and they are in RAID 0, so it actually 1/4).
Leads me to believe that consumers will be disappointed in SATA III hard drives. But they may be faster than SATA II. But they rate them at the maximun thoughput, not real world use.
Get the Samsung Spinpoint F3, others rave about them.