Hello Steve! DBS mod does increase the range, but it does not increase the penetration of the signal. So if you are flying in the field where are not much interference signals, the range will definitely will be increased to 2000m (6000feet) but in the residential area, where are a lot of wifi and other signals the range will stay the same. To extent the range here you need to increase the power of the transmitor so the penetration of the signal will be better. As i know in the US drones are set to FCC mode so you have stronger signal (27dB) than we have in Europe, but i saw some videos on youtube where guy was able to increase it to 33dB by changing a code.
I have DBS antenna on my P3S, and i easily fly 2km outside the city, but in residential area i loose video already at 50m! (150ft) and control goes away at 150m. It is ridiculous so i tried to do the ftp mod but bircked the rc...
So my advise is, if you want to fly really far away in the city - buy a P3 advanced or professional, unless you want to spend hours reading forums, soldering, changing code and etc....