http://anandtech.com/show/9117/analyzing-intel-core-m-performance
This is an awesome article from anandtech about the Core M structure and why the Asus UX305 with only a 800 Mhz CPU outperforms the other Core M laptops with a 5Y71 at 1.2 Ghz and can even be faster than the i5 Broadwell-U cpu.
So it all comes down to how well Apple is able to dissipate the heat and how good their new design of the MB is. To find the optimal CPU for the new MB will require a few reviews and comparing them with each other.
This is an awesome article from anandtech about the Core M structure and why the Asus UX305 with only a 800 Mhz CPU outperforms the other Core M laptops with a 5Y71 at 1.2 Ghz and can even be faster than the i5 Broadwell-U cpu.
So it all comes down to how well Apple is able to dissipate the heat and how good their new design of the MB is. To find the optimal CPU for the new MB will require a few reviews and comparing them with each other.