What kind of speeds are you expecting?
 
 

Just wanted to make sure you understand my question and doors statement:
Although it is a SATA III drive, the sustained drive transfer rates are not any better than that of a SATA II drive. 
 
The drive's interface can handle SATA III speeds, but your drive's internal max sustained data transfer rate is 126MB/s.    
  
 

A few things about SATA 3:
1) If you're using a physical HDD, then the bottleneck is going to be at your hard drive spindle speed. Transferring files to and from 7200RPM drives can get up to 120-140 MB/s. It may help if you tell us the specs on the drive you are transferring files to and from. Or maybe you're unrar=ing a large file. Either way, just because an HDD is compatible with SATA 3 doesn't mean it'll be any faster because the bottleneck is not at the storage controller, but the storage medium itself.
 
2) To the person asking about the Corsair SSD. 355 MB/s is only the theoretical maximum for the drive controller (I don't know what model drive you are using), but there are a few things ton consider. For one, the firmware on the SSD has some overhead, and the SATA 3 controller has some overhead. Plus you have to consider that sustained write and burst write are not the same. If it can reach 355 MB/s on burst, it's unlikely it'll be able to hold down a consistent 355.
Finally, what are you doing with your SSDs that the difference between 270 and 355 Mb/s is really a factor?