The 850 Pro is faster and will hold performance longer vs. the 840 EVO series.
As Premiere Pro video editing hits drives pretty hard, the 850 Pro is much better suited for people reading this hardware forum.
...the EVO series uses a different type of flash memory than the Pro series...it uses TLC memory instead of the sturdier MLC memory found in the Pro models that have DOUBLE the "read / write" cycles of the EVO before failure. The Samsung Pro series and the Crucial M550, ( now M600) are the two SSDs recommended for use in video editing due to their superior controllers and MLC memory.
Thanks to both answers.
I have the 250g EVO SSD and mines has been working fine in my new month old editing rig. I seen the numbers but so far no issues performance-wise. I can say it was definitely a better drive then the initial boot/software ssd by silicon power s70