Over 20 years ago, I helped build curves on the corners of a modular layout--now owned by the Boeing Employees Model RR Club. These were made as a 2-track mainline, with the inside curve on most corners being 6' radius with the outside even larger, using easements on the ends. The center of the curves is super-elevated to 1/8" and can be as complex or as simple as desired. IIrc, an easy way to make the transition is to use strips of cardboard (such as laundries use in dress shirts) built up in layers to get to 1/8" and then stripwood or other material can be used for the center portion of the curve.
To answer the question, they look good with freight cars as well, imo. For model purposes, I would not go higher than 1/8" and the risers can be under the outer rail OR under the outer edge of the ties (resulting in slightly less elevation).
For any O gaugers/O Scalers in western Washington, these modules are scheduled to be at the train show at the Evergreen Fairgrounds, just west of Monroe on US Hiway 2, on this coming February 27 & 28.
