Quick update.
I had some time yesterday evening, so I threw some parts together:
[Link: photos.app.goo.gl]

and I went up to 3.5 miles. I'm sure I could get longer, but that's the longest distance I had readily available around the house.
[Link: photos.app.goo.gl]

I was able to see full, 4MP video out of the camera. No dropout, no lag, no issues.
[Link: photos.app.goo.gl]

I'm sure I could get longer distance out of it, but as the goal of the experiment is to be able to set few cameras at the long distance range, I can't see ever going beyond 5km (3.10686 miles).

Initial trials will be 1,000 yards, known distance range, and stretching it to 1mile (1760 yards) off range.