Sensitivity is NOT the main criteria for selecting an AM BC radio. It is selectivity! Most assuredly, the limiting factor is band noise, and you can present a case where too much sensitivity is a bad thing.
Another issue is directivity. Several companies, Palomar Engineering is one, make amplified, loop antennas which can be used to null out offending stations.
While I admire your quest for a decent DX-capable, AM radio, there is more to it than meets the eye.