How can one compare ARM to x86-64 CPUs?
These are in totally different league.
They really are not that far apart at this point. Apple's ARM designs have made huge gains with each annual generation and Intel's processors aren't progressing at anywhere near the same pace. It's quite possible that Apple will hit a wall around the same place that Intel is now, but given the pace, we (and Apple) will know that very soon if they don't know in the lab already.
On top of getting close to performance parity, the real story is how much more energy efficient Apple's processors are compared to Intel at the same performance levels. Even without hitting performance parity with Intel's fastest chips, it's likely that Apple could deliver a decently performing laptop *now* with much better battery life than a similar Intel-based laptop.