https://www.extremetech.com/mobile/221881-apples-a9x-goes-he...
This year's chip is even more powerful:
http://www.theverge.com/2016/9/16/12939310/iphone-7-a10-fusi...
I'm also a bit skeptical about the emulation part, but if it's less than 10% overhead out of the gate, it should be okay, and I assume Microsoft could continue to optimize it over the years.