The City of Denver and Denver Zephyr each took 16 hours to go from Chicago to Denver. But the Chicago & North Western/Union Pacific route was 14 miles longer, so technically, the City of Denver was the faster train, average 65.5 mph west bound vs. 64.6 mph for the Zephyr. Eastbound, they were faster still, requiring only 15 hours and 38 minutes.
Despite having the “slower” train, Burlington was able to attract more passengers than the UP/C&NW. According to the 1939 Report on Streamline, Light-Weight, High-Speed Passenger Trains, the Denver Zephyr earned about $2.1 million a year carrying about 93 million passenger miles in 1938 and 1939, while the City of Denver earned only about $1.7 million carrying about 70 million passenger miles.