Hey there oldcompgeek and welcome. Well If it were me I would go with the cheapest cooler you can get. Since your runnning 7850 those wont be hard to cool at all. I would go with 120mm rad size. My corsair h50 cooled my 780 really well consdering the size and heat output of my 780. Good luck!
edit: also with out looking at your case specs I would mount it on the rear exhuast that seems the most efficant way to run it for me.