Well, couple of thoughts....

The AR6100 is defined as a "Park Flyer" rx mostly used for small electrics and that means smaller than your Mustang. The AR500 is defined as a "Full Range" rx meaning it can be used for larger models which would be expected to get farther away. However.... the AR500 had some issues and I've never really seen anything reported about a fix, suffice to say it's been replaced by the AR600.

If it was me, I'd put the AR62XX which uses a satellite rx in that model....