When you get down into the milliohm level, battery resistance becomes less important, let me explain: (wall of text warning)
1 foot of 12 gauge copper wire (solid, not stranded) has a resistance of 2 milliohms. 16 gauge wire, 4 milliohms. A 5mm plug connector to the battery would be another few milliohms as would the solder connections to your ESC/motor. So lets say you really go overboard and wire your car for LOW RESISTANCE. Big chunky wires everywhere... well, in a car that uses 6" of 12 gauge wire and two 5mm connectors, and four well-done solder joints from the battery to the ESC, then 14" (super short motor leads) of 14 gauge wire with six solder joints from the ESC to the motor, you've added up to this:
(2 milliohms from the 12 gauge) + 2(1 milliohms for each plug) + 3(3 milliohms for 14" of wire from the ESC to the Motor) + 10(0.5 milliohms per solder joint... I'm being generous here) adds up to 2+2+9+5 = 18 milliohms in your wiring at room temperature.
Seems kinda high, compared to the claimed internal resistances as low as 2 milliohms I have seen claimed a few places. Not much difference between 0.019 ohm and 0.020 ohm.
To measure resistance in batteries with your charger, it's even worse. I can discharge my packs at 35 amps, but my leads are 12 gauge and if each is 18" long with bullet plugs, there's far more resistance in my leads than my pack. As a result, my measured internal resistance can be quite high.
I think that the best packs are not the ones that fight for the lowest possible internal resistance. The best packs have the highest average voltage under load over a full run.