802.11N High Powered card

I am looking for a average of 600mw 802.11n card. What card card I use that has 600mw or above? The distance with other cards just isnt enough.

how about better antennas?

2ft parobolic dishes is the biggest I will go. Its not practical, I shoot from elevator to elevator. Distance is 9-15 miles. For wireless N to operate at high throughput I need at least 600mw with 29dbi antenna(not dual polarity). Whats your thoughts on this?