1. In technical reviews the 850 Pro and 850 EVO kept trading places for top honors in different benchmarks. The 850 EVO can hold its own against the 850 Pro. The reason for that is Samsung released the 850 EVO after the 950 Pro. The EVO has a newer controller and firmware. Both models use the same 3D V-Nand flash memory.
2. Both models have excellent track records. Absolutely no problems, issues, glitches, or hiccups. Just about all of the problems I see in the forums for ssd's in general are either due to a user's lack of ssd knowledge, incorrect BIOS and/or system settings, and unsuccessful attempts to clone an existing drive to a new ssd. The biggest problem is with the cloning applications. That's one reason why a fresh clean installation of the operating system is the preferred method. The other reason is that Windows does not do a very good job of deleting old, useless files and registry entries. No point in cloning all that useless data to a new ssd.
3. When Samsung originally released the 850 Pro it came with a 5 year warranty. Then Plextor released an ssd with a 10 year warranty. Plextor advertising claimed 1.5 million hours MTBF. Samsung immediately increased the 850 Pro warranty to 10 years to match Plextor. If it hadn't been for Plextor, the 850 Pro would still have a 5 year warranty just like the EVO. There are no other consumer ssd's with 10 year warranties.
4. The usual suite of synthetic benchmarks can be deceving to anyone who is not familiar with them. The first and biggest problem is the benchmarks are designed to grossly exaggerate very minor performance differences between models. The graphs and charts in the technical reviews reflect those minor differences. To the uninformed those colorful charts make it appear as if there are very large differences when in fact the differences are almost negligible.
5. Typically an EVO model costs less than a Pro model and represents a better value for the money. However, there may be special sales coming up with decent discounts on the 850 Pro too.
6. Most consumers would not be able to notice or "feel" any performance difference between the 850 Pro and EVO. Someone would have to be doing some sort of professional work that involves a really heavy workload. Gaming and editing family videos do not count as heavy loads.
My comments are based on a little bit of logic, common sense, and experience. Of course there are times when logic does not apply. Sometimes a person simply wants bragging rights.
I maintain an ssd database listed in a sticky at the very top of this forum section. Here is the link:
http://www.johnnylucky.org/data-storage/ssd-database.html
Scroll down to the SATA 3 section where you will find the 850 Pro and EVO. Follow the links to the technical reviews. The reviews are in English and many other languages.