Yes, you are probably wrong. Could you please explain what you mean by a 6x controller? SATA III at 6 Gb/sec or an add-in controller that uses 6 PCI-E lanes?
If the former, as I've said before, a controller is supposed to be able to drive all its ports at speed. If the latter, since this is a mirror (RAID 1), it doesn't need to get the data over the PCI-E bus twice, since it's just reading it twice.
Legend has it that RAID 1 writes only slightly slower than a single drive. You do have to wait for both disks to report the commit, even if the same write was sent to both at the same time. So the slower commit always controls. Legend also has it that some RAID controllers will split the reads between two drives in RAID 1, increasing your read rates, especially in random reads. Imaging one drive seeking the next read while the other is giving you the data from your current read.
@eduello, it may have been an accidental double-post. Don't sweat it, the moderators (me) clean up doubles once they are pointed out to us.