12.3 is available in Corsair SSD toolbox for me now. Must have happened in the last couple of weeks; I can't recall exactly when I checked last, but not long ago. I saw the upgrade in version 1.2.5.5, but had to upgrade to 1.2.5.7 to have it succeed. It also updated both my SSD's at the same time.
Any improvements in read/write speeds look to me to be within the margin of error of CrystalDiskMark.