How large is your loop, and how long does the consist take to complete a circuit? It might be running faster than you think!
I remember the first time I ever saw the video feed from one of those camera cars, that provides an “engineer eye” perspective of the layout. It looked like I was riding a roller coaster! Bottom line, the top speed of the prototype is kind of irrelevant. On a small layout with train set curves, 60 mph or even 45 scale mph is plenty fast. What’s harder is getting smooth, realistic slow speed performance.