I've found a study out of the Netherlands which actually measured the receiver sensitivity of 10 each car radios, portables and handhelds. Sensitivity was measured for 20db Signal to Noise Ratio and 46db. The testers generated a stereo signal that was either directly fed into the receiver antenna jack, or indirectly fed (and then a factor was applied for the losses). Any radio that could not generate a stereo signal at those levels was rejected and not measured. At the end, 9 car receivers were included, along with 5 portables and 6 handhelds.
I suspect that the results are probably more accurate and real world useable than manufacturer supplied numbers. The measured sensitivity was in dbuv, and I converted all of them to uv. I also did some rounding so they're not exact (but they're pretty close).
Here are the results, which are the voltages applied to the input of the radio to generate signals with the specified SNR's.
Car Radios (9 in Total)
20db SNR: Average 1.3 uv, Best <1.0 uv, Worst 6.3 uv
46db SNR: Average 80 uv, Best 56 uv, Worst 800 uv
Portables (5 in Total)
20db SNR: Average 4 uv, Best 2.3 uv, Worst 5.6 uv
46db SNR: Average 100 uv, Best 56.2 uv, Worst 141 uv
Handhelds (6 in Total)
20db SNR: Average 8 uv, Best 2.3 uv, Worst 28.2 uv
46db SNR: Average 400 uv, Best 200 uv, Worst 1000 uv
Some Considerations
No home stereo receivers were tested, although they more than likely rival the car receiver results. That has to still be verified.
There was one car receiver that tested very poorly and it somewhat skewed the results. Most car receivers were around the 1-1.5uv sensitivity mark for a 20db SNR. A few were under 1uv.
Typically, portables did much more poorly than car receivers, and the handhelds performed more poorly than the portables (although one handheld, the Sony ICF-C1200, rivalled the portables. Interestingly enough, the worst handheld was also a Sony, so name brands are no protection against bad radios. The best portable was a Sony, the CFD-S550. The best car receiver was the JVC KS-FX480, but there was a Kenwood & a Blauplunkt that rivalled it.
I'm struggling a bit right now to make sense of these numbers, as I have no good idea of what a 20db SNR sounds like (nor a 46db SNR either).
It takes a much greater field strength to get that 46db SNR. If you take the average for the portables - 100uv - then you only would be able to get that type of signal at 3 meters from the transmitting antenna (if you're running at 250uv/m at 3 meters). Obviously, you can hear that signal much further than that with decreasing SNR - a sensivity of 4uv with 20db SNR (the average for portables) translates to a range of 75 meters or about 250 feet.
Anyway, I just thought I'd throw this out there for discussion. No major surprises, just more grist for the mill.