The 850 EVO series aren't affected afaik and apparently Samsung came out with firmware updates for the 840 EVOs.
Then you should visit OCN and see the results of that so-called "fixed" firmware

. Many still have severe drops in speeds despite their Magician software loading into memory to constantly refresh the old data. Samsung's problem is that they used poor quality TLC NAND which is atrocious and not worth risking any of your work on.
People only found out about their problem product some years later after it was released everywhere, and more people still kept buying their dodgey gear. Word to the wise, don't buy any of their SSDs ever, because you have other manufacturers that have a fine history of quality hardware releases such as Intel, plus their warranty is far superior than Samsung's when it comes to anything related to their SSD's.