What comparison? Where did you find that someone got COD5 to run on high at that res? (which isn't astonishing, it just depends on hardware) Why is it that if COD5 runs, so should san andreas? I don't understand your logic or your question.
I'll have to admit though, until now I thought you meant GTA4. I'm not a fan of the series and don't know it well. In that case, the 4670 will do just fine.