I can already tell you that the EM-406 (plain, not A version) quits above 24km, at least in one test.
I hadn’t heard of the NEO-4U unit, I’ve mainly been looking at modules that have built-in antennae or at least an easy connection rather than having to route RF on the PCB. But I guess we’ll look into those if none of the modules we’re trying end up being satisfactory.