I think it's the drivers. I've seen both 3985 and 4014 up close. They are massive but the drivers aren't huge. I think 80 inch drivered Northerns seem so massive because of the wheel size. Standing next to a wheel that is taller than most people has the effect of making machinery just feel that much larger.
Exactly! The UP Challenger has 69" diameter drivers (only five feet nine inches), while the 4014 is only 68" diameter drivers. A Northern type, or Hudson type, with 80" diameter drivers (almost six feet eight inches) is visually so much taller, everything tends to look even more massive.