Airport Extreme Wifi Limited Speed

I have a prior-gen Airport Extreme, with 802.11n 5ghz/2.4ghz. My ISP just bumped my speed and I've noticed a new, odd problem. I haven't found anything related to it when searching, so I'm hoping someone here may have some ideas.

When I connect my Macbook Pro to the Airport via ethernet, my download speeds clock in at 110 mbit/s. When I connect my MBP via wifi, the speed drops to a consistent 60 mbit/s. Both of these limits are definitely upstream of the MBP; I measure the same ethernet speed from my desktop, and the same wifi speed from a Windows laptop.

The odd thing is that the 60 mbit/s cap only seems to apply when I'm connecting to something on the internet. I can copy files locally over wifi at 160 mbit/s or faster. It seems like there's something specific about routing data from wifi out to the internet that slows things down on the Airport. I'm running the latest firmware, and IPv6 is disabled.

I can definitely live with this situation, but I'm curious nonetheless. Does anyone know what might be going on, and how to address it?

 

I definitely expect Ethernet to be faster, but that's not where my question lies. The local file copy over wifi, which ran at 160mbit, shows that the wifi bandwidth is not the problem. My MBP can definitely talk to the airport faster than my internet connection speed. My question was (perhaps unclearly), since my MBP can communicate at that faster rate, why is it getting slowed down so much only when heading out on the wan port?