@Hot Water posted:
Yes, markedly "over 100 MPH". Stories are legendary about them handling long heavy passenger trains, cruising at 100+ MPH. What with their running gear design and high boiler pressure (which also provides very high superheated steam temperatures), they would be easily capable of 125 MPH. I know that the UP FEF-3 class 4-8-4s were tested at speeds over 120 MPH, and although pretty similar to the Santa Fe 2900s, they were/are without roller bearing side rods.
The 2900s came from Baldwin with plain bearing, tapered rods. They got Timken roller bearing rods in 1947. ATSF rated them at 90mph prior to the Timken rods. After they were upgraded they got the 100mph rating.
Fun trivia bit: the rods removed from the 2900s were passed down to the locomotives in the 3751 class.