I've used quite a few different (somewhat affordable) wireless video transmitters, and the one that seems to be most consistent with long range has been the Connex Kits. There is a full size Connex version capable of 1,000m LOS range, and a newer Connex Mini that transmits 500m LOS range (that's still quite a distance!). There are some short comings to the Connex system when using it for video cameras, as these kits were originally designed for Drone use streaming full 1080p up to 60fps.
Some of the cons for on-camera video use are that it requires a battery, but there are no battery mounts. Also there are no standard mounts to attach to your video rigs. Finally it doesn't transmit audio (if you need this). But for distance, reliability, performance, and price the Connex kits are darn good. To make life easier, Camera Motion Research created a special frame and battery kit for us shooters.
The latest mod for their Connex Mini kits is adding an SDI to HDMI converter. This allows someone like me to now use the Connex Mini kit with professional cameras that only offer SDI out, and does it in a clean, simple, and easy way. All of the new hardware is still within the custom modded frame kit, and it's all powered by a single cable (via D-tap).
I'm often running Multicam Live Switching at events and one of the biggest headaches is runnning SDI Cable across the floors. It's not easy running cables and taping them down. This also prevents the cameras from being mobile. But with a wireless video kit, you can move freely around the event. With this new mod, you basically have a tiny high performing wireless HD video kit that can support both HDMI or SDI inputs. Here's a test of latency below.
Keep in mind that in my latency test, the Connex Mini does not transmit audio. My audio source is coming in from another input into the ATEM Switcher. Both feeds were recorded to a Hyperdeck Mini and you can see it's just about perfect in sync. With this type of setup, that camera is now free to roam up to 1600 Feet away from the receiver, and we can still Live Switch during a Live Production.
If you are working with the Connex Wireless HD Video kits, and you experience latency, that could possibly be caused by your camera's output. Some cameras will have a 3-6 frame delay and you'll notice this when connected to any monitor. I personally have moved to working with the Ursa Mini cameras for my Live Production, as this camera offers almost no delay on SDI output, and with SDI I can do long runs up to 300 feet (HDMI limit is around 12 feet).
You can find out more about the Connex Mini kits over at http://CamotionLLC.com