Forget the math and test what you run. That tells you what you can or can't get away with; for sure 
Grades are a lot of "throttle work" to run in conventional once the intrigue of the grade challenges fades. I kinda quickly ended up with 4 blocks on a Z, one throttle per wall to run one line "no handed" around a 12x15. (two 15' walls hold the 7" rise and downhill (1.5% grade difference off ceiling between these east/west walls), short wall tracks hold mostly level track, but a ¼" rise on each end too; the 1st transitions)
Rises in curves don't play well with unsprung axles ; Tri-podding happens. So in a curve go flat or very lightly graded < ⅛" or super elevate (even more transition math; oh boy 
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Think about "old rollercoaster rails"(before tube type), note you got positioned for a curve before it happened. All to keep the car(s) flat and stable, always 4 wheels on track. Bending rail up/dwn/left/right evenly is easy. Use super elevation if you must rise more than 1/8" in a curve. (Eyeballing it in would be better than nothing 
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