Many thanks to SWLing Post contributor, Ivan (NO2CW), who writes:
I ran a test of weak signals RTL-SDR v4 against Airspy HF+ Discovery. Using sdr # and a few gain adjustments particular to each of the receivers. I ran the test at approximately 9 pm local time using the same W6LVP loop antenna from my location near Miami Florida and I was intentionally looking for barely readable weak signals. The RTL-SDR v4 is a great budget SDR receiver!