Samsung has released a newest firmware update for its 840 EVO series solid state drives which should fix the issue of low read performance with older data on the drive.
Marked as version EXT0CB6Q, the new firmware can be downloaded and pushed to the SSD via Samsung's own SSD Magician software for Windows. Samsung has also provided bootable disc images which allow you to update the SSD without an operating system.
Of course, bear in mind that you should backup everything before updating.
TechReport.com, did a quick test of the new firmware showing that it does indeed improve read performance of older data on the drive.
Source:
via Techpowerup.com.