It's difficult to answer your question without knowing more:
Weights of cars;
Rolling resistance (it matters, no matter if rising on a grade or descending);
Heft of the locomotive, or if there is to be more than one locomotive, the heft of each of them;
The types of couplers (this matters because mixed 'n matched couplers don't do well 'shoved', which is what happens on descent); and
The grade, and if there are curves during the descent or ascent.
All these factors have a bearing on how successful any one track arrangement will be, and only for the consists tested. Make up a different train and all bets are off!
In the real world, only heavy tank rodded steamers would be able to climb 5-12% grades, and then only with very limited trailing tonnage. Or, it would have been a geared locomotive such as a Heisler, Climax, or a Shay. Diesels are like those latter three for the same reason: the weight is all on driven/geared axles, providing maximum braking and tractive efforts.
Helices require great skill and care in design and construction unless you don't mind getting into one several times each session to fix something, like a derailment. The shorter the radius, the less high the coils are overhead, the steeper the ramps/coils, the worse it will be. Unfortunately, the more separation you want overhead, the steeper the ramps have to be, defeating yourself and your trains.