Tractive effort & unit price were considerations of W.P.'s mechanical dept. The W.P. did come close to buying SD-45's after tests with EMD demos, but GE cut them a better deal on U-30B's. Seems GE wasn't as fussy about the condition of units traded in; they even re - used the Blomberg trucks so W.P. mechanical crews would be familiar with the pieces.
Recall that W.P. allowed almost all types of Ewe - Pee pool power to run through; 6 axle EMD's & GE's were frequent visitors to the Feather River Route from the early 1970's on, as were BN EMD's & even 6 axle Alco's. Espee trains detouring over the Inside Gateway, as well as those on the paired track in Nevada, were powered by 6 axle EMD's almost exclusively from the late 1960's on.