if you look at an Official Guide from the mid 50s (when the Q was very well maintained) you will see that the Denver Zephyr left Chicago after the CZ and arrived Denver before it. I take this to mean that the DZ was the racehorse passing up the CZ during the night. I can say that in the early 60s when I was on Burlington trains (including excursions behind 5632) we didn't tarry. I was in the vestibule w/ the rear brakeman who was timing '32. We were doing 90.