@jackson, yes, lower frequency generally has longer range for a given power, and also greater opportunity for inbound interference from other transmitters, intentional or not.
On the other hand, you can do 2km easily with 2.4 GHz WiFi if you were willing to put antennas on large enough poles to get the path high enough to remove terrain effects, see Fresnel zone.
This lets you optimise for whatever you like doing most; putting up masts, using special antennas, or selecting well designed radio modules.
Using 2.4 GHz WiFi may also get you a bit more data security. Depends on how important that is to your application. There's an amazing amount of telemetry about that has no security at all.
There's a few services available from 2.4 GHz equipment suppliers; check out https://airlink.ubnt.com/ ... pan and zoom to your location, put the pins in, choose frequencies, and you'll be given link quality estimates based on a digital terrain model.