There is a new firmware version EXT0CB6Q available for the Samsung 840 EVO series. This version is NOT shown by the Samsung Magician Software (at the moment). It is part of the "Performance Restauration Software", which must be downloaded from here: http://www.samsung.com/global/business/s.../downloads.html
This firmware and software is a fix for the drop of read speeds down to 30 MByte/s or less of older data stored on Samsung 840 EVOs. I have applied this new firmware to my 840 EVO 500 GB without any problem, although the Z77 chip set of my mobo is in RAID mode, not in AHCI. But the ssd is not part of a RAID.
(see also: http://www.heise.de/newsticker/meldung/F...ar-2424150.html [german])

Greetings
Torsten

This update won't corrupt any data on the drive? I have 2 months old 840 EVO.. better be safe than sorry :)

I have applied new firmware to my 840 EVO 120 GB (Windows XP 32 bits)

It took 5 minutes to 4 Gb of data

Link: http://www.samsung.com/global/business/s.../downloads.html
"Samsung SSD 840 EVO Performance Restoration Software"

Before and after new firmware:

There is a new firmware version EXT0DB6Q for the EVO 840 series available, which supports Advanced Performance Optimization in Magician 4.6. The download can be found at: http://www.samsung.com/global/business/s.../downloads.html

Firmware update does not work on AMD systems with AMD AHCI drivers. You have to use MS standard AHCI drivers.

Installing the Performance Restoration software, than running the program, caused it to corrupt my Windows Boot Manager. Is the new 'advanced' tab in Samsung Magician, similar to what Performance Restoration does?

Since April '15 there is a new firmware, along with a dedicated Samsung Magician 4.6

http://www.samsung.com/global/business/s.../downloads.html

could be interesting to see if there are further changes with this.