I suspect it will make 5 as well.I suspect those 120V mph numbers for the Model 3 are understated.
A Gen 1 Volt charges at nearly 4mph on 120V 12A and the Model 3 is ~24% more efficient that the Gen 1 Volt. So unless there's something weird with Tesla's charging systems, a Model 3 charging at 120V 12A should be closer to 5mph than 3mph.
If voltage doesn't sag, I actually now[1] get ~4 from my model S 85. Did it last night as a matter of fact. Right at 12V/12A under load and was pegged at 4MPH charging.
[1] This may indicate recent improvements in low-power mode on the car. While I've charged on 120V circuits previously, I'd ususally get more like 3.5 MPH, which the car would round down to 3 on the display. But then again most of those times the voltage also sags a bit. Last night was the first time I've used 120V at home (where my unloaded circuit voltage is about 122V) in a while, and I saw 4MPH on the display.