Hello, We have the same setup but only about 500ft between our links. I always get 300mbps up and down which is awesome.
And yes, its overkill for such a short distance, but next year, we will switch it to a new building further away. baby steps, i guess ;)
Anyhow, I did the Google Earth setup that Aruba has where they can show you an estimated signal propagation from those antennas/APs/degrees of placement, ect. My map showed me a signal of 6mps, in channels 149-165, pure N, 40mhz, at about two miles. Of course I cannot verify how far they go (unless I mounted the mesh point on a golf cart and took off ;).
I would rig them up and configure them, and at the very least, you can test them in AirMonitor mode to see channel interferance and noise levels accross the channels.
See if you get lucky with a link. have one person at each antenna on the phone with each other adjusting until you get your best signal.
Good Luck