Which card is faster may be irrelevant. Since the 5 series is newer, it is likely to be more supported on your system than the other option. I have given you all of the opinions I can give you here. Without actually benching them both, on the same system, there is no way for me to know which will perform better. This may be a question better suited for a GPU manufacturer. If it were me, I would pick the tech support of my favorite GPU manufacturer and email them the question. You should basically give them your system specs, price point and ask them for their suggestion on AGP vs PCI for your build. I am interested to know the results.