We tested the 6670 here at 1680 x 1050 at the highest settings, with 4x anti-aliasing, and still managed to hit almost playable framerates on some tough games. Drop some of the GPU-intensive settings and you'll be happily gaming with the AMD Radeon HD 6670.
That said, the XFX Radeon HD 5770 is a real budget gamer's card, and beats the 6670 by some margin.
DirectX 11 gaming performance
DirectX 10 gaming performance