The cost of going so high is a steeper climb for your locos. If you have limited space, I would stick with the 5" range. That's roughly plate H for current railroads anyways.
The tallest stock 3-rail freight cars I can think of is the MTH premier husky stack. 5-9/16" - definitely higher than the prototype.
Unless you have tons of space and can keep your climb under 2%.
Originally Posted by Bano7384:
Sounds like a plan. 6" it is.