Although I'm primarily in O gauge, Standard Gauge has been in the family for 40 some years. Not once in that time did we (my dad & I) try even the slightest grade. I've never seen more than a L" or 2" rise in any layout - and that was at the National Toy Train Museum with the train climbing and descending ramps to cross a tinplate bridge.
I'd test it myself but all those trains are packed away at the moment. My equipment is the smaller series stuff, like #8, 10, and 318.
Anybody out there do grades, or even an over&under figure eight?