I’m not saying that the Eastern Express to Walden is bad but it doesn’t cut off climbing. In fact, it’s a steeper climb. Pueblo and Fort Collins are of similar altitude. It takes 125 miles to climb to the top of Hoosier Pass from Pueblo which is about 10,000 ft of climbing. That’s about 80 feet per mile. It takes 66 miles to climb from Fort Collins to Cameron Pass which is 7800 ft of climbing or 118 feet per mile. That’s a significantly steeper climb.
I haven’t looked at Peak, Parks and Prairies specifically but the Gangplank in Wyoming is the reason the rails went that way initially. The Colorado mountains are too steep for rail and they do have significantly more climbs.
I’m not trying to dissuade you from the the Eastern Express route but only to inform you that there is no free lunch. Colorado’s mountains will get you one way or the other