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.
The Radeon HD 7770 will give you good performance on 1600x900. However, the Radeon HD 7850 will provide even better performance and it will be a little while longer before you will feel the need to upgrade.