Old debate and the clichés rise like zombies from the grave. It depends on the intensity of the incident. You may not be able to do the job with eight
if you are lucky enough to land in a serious rampage with multiple shooters and distance. If it the single mugger who stands in front of you and announces - I'm going to mug you! - then 8 might do it.
You have to determine the risk cut off for gun fight intensity that works for you. Or you can just say clichéd items - as repeated since the Internet was invented by Al Gore.
To be pragmatic for me. A semi and an extra mag or a revolver and two speed loaders is where I make the cut when I am out.