I would use a single TV and a new factory made cable to test your antenna. Connect directly from the antenna to the TV. Too many unknowns in using old, existing, weathered cabling. And cable components like splitters and boxes are not compatible with over-the-air TV signals. Once you find what the situation is, you can add amplification as needed.
I own an Antennas Direct DB8e and am very happy with it. The DB4e is basically 1/2 of the DB8e. I know nothing about the Mohu products, but I'm put off by the Mohu site and the marketing oriented descriptions of their antennae. I would prefer to see real technical specs, like they have on the Antennas Direct site.
Here are the tech specs for the DB4e -
http://www.antennasdirect.com/cmss_f...s/DB4E-TDS.pdf - if similar info is available for the Mohu products, I don't see it on their site.
Personally if I had $150 to spend, I would go directly to the DB8e. I could point the panels in different directions and see how many stations I could pick up by pointing the panels at the local cities (Lexington, Chapel Hill, Raleigh, Fayetteville - all have groups of stations on your plot). Your report is not very favorable, and I'd go for the most sensitive antenna I could find.
If you want to get WTVD from Durham, you'll likely need a dedicated VHF-high antenna, or a multi-band antenna, pointing at Durham. The DB4e and DB8e are only UHF, channels 14-51.
Looking at your plot, there is only a moderate amount of signal to be had at that height. If you go higher, it might get better. But surrounded by trees could be a real problem for reception, and you may never get good reception for more than a few stations unless you get above the tree tops.