Rush hour traffic in New Orleans is quite uncomfortable for people, but it only has two of four difficulties for cooling systems. These are:
1. High temperature
2. Low humidity
3. High altitude
4. Low airspeed
If you want a REAL test, try a high altitude desert pass in summer. And enjoy the white smoke and snot in the oil cap you'll get from it.
If your fan is drawing a lot of power at low speed, THAT'S WHAT IT IS THERE FOR. You need the airflow. And why the HELL do you care how much "power" you get in stop and go traffic? As for the mileage claims, you'll do a whole lot better if you don't fly up to 30 MPH in 5 seconds and then jam on the brakes.
Remember, 100 deg ambient temperatures are BALMY for an engine with a 195 deg thermostat. Humidity effectively dramatically increases the effectiveness of a radiator; it's like doubling its size if no other variables are changed. Running at 6000 feet instead of sea level is like chopping 30% of your radiator off, for comparison.