Heh, yeah, you'd need that power in that environment. We did our test between the roof of a 16 story bldg, and a school yard playground set that had a favorable terrain profile. The next year, the company deployed wifi in the 16 story bldg, and we couldn't make the same link from half a mile away. I really didn't want to use a power amplifier because our company execs were in the top floor of that bldg, and I didn't want to have to explain to them why they couldn't get their wifi.

For the shorter 8 mile links we have a ham with a 70ft tower on one side of a lake, and the ground site about 15ft AGL, at the end of a tributary. Might not be able to make it work if we didn't just happen to have the favorable terrain.