Which video card is better?

i would go with the HD 5770 .. Even though the HD 4850 has more bandwidth to its RAM (i guess you call it), it lacks in many other features that you might enjoy. The 5770 has smaller transistor size which makes the GPU more efficient, 5770 supports DX11 and 5770 has GDDR5 RAM instead of GDDR3 (which might help compensate for the lower bandwidth of 128bits). And I can tell you from personal experience, 5770 will run those games in max. I have played fallout and black ops in max (but on a slightly lower res than 1080P cause my monitor supports it) but I feel the 5770 will perform in a more favorable way than the 4850