My late Uncle George, a WP engineer told me he had the Zephyr doing 100mph in some places between Portola and Winnemucca. Early in his career he was firing a newly shopped passenger engine and noticed they seemed to be clipping by the telegraph poles at a pretty good rate. Checkiing his pocket watch showed the train doing 105mph. This was coming down the valley between Marysville and Sacramento. These were the times when they had section crews maintaining their "sections" to perfection. While these times were not official, on occasion they did happen. Hope this partially answers your question.