Millenicom 4620 Hotspot. In order to set a baseline, I took a reading using Speedtest.net before leaving the house. The Hotspot was indicating 3 bars of 4G and the test indicated 20Mb/s download and over 7Mb/s upload. Pretty good if I do say so myself.
It appears that signal strength does not have as much impact on speed as I'd anticipated. Further tests suggest that it may be related to time of day or luck of the draw for the ISP the hotspot uses. It took several tries when we got home to connect to the specific ISP used for the baseline test, and the afternoon results were notably slower than the morning. We'll see if there are other factors we can control as we get more experience with the Hotspot.
Fire Control Road (NF-64) is 10 miles of gravel that connects Highway 87 to the Houston Mesa Road. There are several spots at the western end that would be viable. The one I liked is south of the road about 100 yards, about 2.5 miles from the intersection with Highway 87.