3 ohm vs 1.5 ohm ignition coil

OK, so on my slant six I was running a 3 ohm Pertronix coil, no ballast resistor, with factory mopar electronic ignition. I'm swapping to a v8, and I read on the Pertronix website that the 3 ohm coil is for 4 and 6 cylinder applications, but for a v8 one should use the 1.5 ohm coil? Am I not OK with my 3 ohm coil, should I switch to a 1.5 ohm coil? If so, why is that true?

Brian