My observation is that Apple is extremely stingy with the amount of RAM they put in their devices, throughout the range; I had to buy a top of the line Macbook Air back in the day just to get moderately future-proof 4G, which I would have considered insufficient at the time in a PC laptop. I wouldn't be surprised if there's cliff-edge effects on performance when they start optimizing later software for hardware that has more RAM than the previous generation.