John....I believe m/kwh is the best way of measuring efficiency. Whilst it doesn't directly give you actual miles, we know that a full traction battery has roughly 13kwh of usable power. So multiplying trip m/kWh by 13 gives a good indication of actual miles.
The range of the NX from Lexus is in excess of 40 miles, plus all the usual caveats of how it's driven, conditions etc. Various independent reviews have backed that up, some getting a lot more than that in favourable conditions. Before this current milder spell I was getting about 2.7 m/kWh though last night on a 10 mile return trip I saw 3.3 m/kWh which shows how variable it is depending on conditions. 2.7 m/kWh is roughly 35 miles and 3.3 about 43 miles.