Kind of irrelevant when you should never put yourself in a situation with that much of a load and a 17ft run of 8gauge wire. And anyone running something that is capable of a continuous 70amps of current for that long is going to be running 4gauge wire more than likely. I mean, it's good to show the absolute limits of things, but it's no surprise that CCA vs OFC of the same strand count is going to favor the OFC. When you get companies like Knu who oversize their CCA, then the benefits get smaller and smaller.
Power lines are aluminum. But it has nothing to do with it being a better conductor. It is just way cheaper. This is also why they run very high voltage - so the current is less, and the efficiency is way up, even though the conductor has a higher resistance they can use smaller wires.