I had replaced two of the steel wheels on my 2016 S with much lighter versions last September (Enkei RPF1s), but didn't really see an efficiency improvement then. I put it down to new tires having more rolling resistance than old tires, and the weather cooling off.
In March of this year I replaced the other two wheels. They're around 7.5 pounds lighter per wheel than stock. Partway through April I noticed my efficiency numbers headed towards the upper 4.x m/kWh range (I reset all those counter at the end of each month).
Admittedly I'm driving less now, and more of it is 'elective' as opposed to necessary (no more commute). The elective nature means I can be in less of a hurry. For April I averaged 4.9 m/kWh, over 234.4 miles. My previous best had been last May at 4.7 m/kWh.
Keep in mind that I've done a bunch of other weight-reduction efforts. Not going into full detail on that here, but (for example) one of the larger items on that list is the 12V battery tray, which because I reduced my battery size/weight down (via LiFePO4 battery), I replaced an over-four-pound set of parts with a ~170g setup, a weight reduction of over 10x.
I went for a short trip today (under six miles), with the counters starting at zero (first day of the month), and was able to get 5.3 m/kWh. I've never seen 5.x before today. This trip had hills even. And this is a round trip (started and ended at home). I was intentionally trying to get a good number, so my more normal driving style wouldn't do as well.
Feel free to contribute your numbers here!