If 4670 is comparable to 3870, while it is, then it's comparable to 2900xt 1gb. My friend has 2900xt 1gb and I can tell that all you need is a strong cpu. Yes, you will make use of that additional ram and really, does ram speed affect in-game performance? I don't think so. From what I've noticed, if it's not too slow, and that ddr2 will not be too slow, it doesnt affect it by more than 3%.