ARM chips in current mobile phones and tablets have those penalties, which slow them down in benchmarks.
Apple designed the memory controllers for many of the PowerPC Macs, and they were no slouch in memory performance (given the process technology at that time). So there's no reason that a 64-bit ARM chip specifically (re)designed for a laptop by Apple won't have a laptop class memory system and laptop-sized heat sink, thus massively increasing system performance as well as top-end clock speed over the mobile phone chips. There's likely nothing in the logic design of the arm64 CPU cores in the A8X to prevent that, and Apple has enough engineers to tweak and tune the physical design and layout for a hotter process....
...assuming they actually want to do such a product, and not just put a lot more heat on their current supplier, Intel, to keep up with the roadmap.
