HD 7770 vs HD 7850 at 1680x1050

I am looking to build a budget gaming PC here is the build so far (ignore the 7850)

http://pcpartpicker.com/p/whkf

I already have a chassis, monitor, os, HDD, and optical drive.

I am looking to play games like Bioshock, Battlefield 3, and Guild Wars 2. I want to play at settings that are a mix of Ultra/high/ and some medium if necessary. I'm basically wondering if the 7850 is even worth the price jump at these resolutions.