If your in need of some performance boost. I would recommend upgrading your 5770 to a 6870. It offers a substantial performance boost while using only 43 Watt more power;
While the 6870 may be last generation, it's proving to have great price & performance ratios while also offering much more performance for the money than what's available in the current generation lineup. But because it's last generation, it's drivers are also that much more mature.
Depending on your Power Supply, a 6870 may be the way to go.
5770 vs 6870 specs [look at power consumption]http://www.gpureview.com/show_cards.php?card1=615&card2=635
5770 vs 6870 Benchmarkhttp://www.anandtech.com/bench/Product/538?vs=540
XFX 6870 1GB [Price $189.99 + Free Shipping / Before $30 Rebate]
Reason: This XFX Model may cost $10 more than the other 6870s after rebate, but I feel the dual fans will disperse heat faster and more efficiently during load operations.http://www.newegg.com/Product/Product.aspx?Item=N82E16814150521