First off, you have clear line of site? If so, then have you decided on either using the 2.4ghz or 5ghz for the PTP link? I would think you can use any of Cisco's yagi antennas for that distance, but you would need to decide if you want to use the 2.4ghz or 5ghz and if you plan on using all 3 antennas or just one.
-Scott
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