which model, 13-in or 15-in?
Main speed differences may be due more to 'number of antennas' that to chipset. The 13-in models may have fewer antennas. All of this is completely dependent on your field conditions and channel usage, including distance to Router, competition from neighboring Routers, channel selection, and interference.
For example, the baseband speed in the 2.4GHz band is about 54Mbits/sec. To get faster speeds there, the data are sent as the difference between signals on multiple antennas. [This is thinkable for the difference between two antennas, but gets really messy when trying to think about three antennas.]
5Ghz is a comparable situation but has faster baseband speeds are possible.