Hmm it might be me, but I would stick to the 560, I think that by habing 2 550 their power cannot combine, they would work separately liek two GPUs. (same case with a i7 3.0Ghz for example, it runs 3.0 ghz each core not all cores altoghether like 8x3.0Ghz = 24 gHz.) So I think a 560 MSI OC would get you a better performance in the end. But this is just me, if anyone out there who knows this better may actually give you some more reliable advice. Or just do as Dave said and get Google and research on your own.