Greetings one and all it has been a long time!! Anyway, I use the MIDI-JET PRO which is rated at a distance of 500'. Granted that is probably based on having a perfect "line of sight" between the reciever and transmitter. The KENTON system is rated at 50'. I "field tested" that concept with the MIDI-JET PRO at an outdoor show and was able to work roughly 150' feet away. As I got farther away, there was a delay in the info getting out the reciever. And that included putting the reciever on a cable in front of the area/stage where we were playing. One thing that does help with this... If your using in-ear monitors you won't have the delay both systems usually do a good job tracking the RF signals.
Another thing to remember with wireless MIDI. It operates (like wire-less internet) in the 2GHz frequency range. Wireless in ear systems and microphones operate in the UHF ferequency range (600 - 700 MHz). For those who don't know, the lower the frequency the farther the signal will travel, the flip side to a higher ferequency it penetrates walls better but gives you a shorter distance. There are even some wireless systems that are in VHF (170 MHz). Most "pro" systems are in UHF though. VHF systems are prtty much a thing of the past. I am not sure how long it took before the first high end gig head cab comany radio traffic. It's all fun and games until you hear..... "and the winnder is.......<lots of static> "CAB 225 to DISPATCH, where's my pick up at!!"
Anyway, that is my $ .02 As always if I have missed something, some else please chime up!!! HAPPY NEW YEAR, Mark!