Actually, now that you mention the $75 difference, I went back to your first post and it turns out you were talking about the 840 Evo compared to the 850 Pro. Sorry, somehow I misread that and thought you were referring to the 840 Pro.Thanks for the clear answer. The markup in my local store for the 850 is around $75 so I think I'm gonna go with the 840. My first SSD!
Not that it'll change your decision to get the 840 Evo. That's an outstanding SSD for the value.
There's a bigger performance gap between the 850 Pro and the 840 Evo, but unless you're looking for maximum performance, there's still no reason to go for the 850 Pro.
Enjoy your SSD.