Simple Upgrade question

First off, here's my current specs:
Microsoft Windows 7 Ultimate 64-bit on a 240GB SSD
AMD Athlon II X3 445 Rana 3.1GHz
4GB DDR3 Ram
ATI Radeon HD5770


I'm here for a little advice. I just plan on upgrading a few or single parts just to increase my performance overall. In games like Battlefield 3, i normally stay at 30-40 on Medium settings on the highest res, so I want to increase that performance overall.

If I were to upgrade my GPU, which would be the best upgrade from a 5770 for the price? And since I'm 64 bit, would it be worth it to buy more RAM?