ChuckAllen, TX
That depends on what length cars you will be running. Transition-era 40 and 50 footers will be happy with the lowest frog number Atlas sells. More recent goods vans may not be. Full-length passenger cars or 89 foot humonguboxes with body mounted couplers won't be.
Locomotives also enter the equation. A train of ore jimmies can take a streetcorner curve and would probably operate on #3 turnouts. Since their usual motive power was either a 2-8-8-4 or a couple of six-axle diesels...
Best way to find out. Tack a couple of turnout templates to a flat surface, then bend flex track over them to simulate the different possible routes. Push and pull your rolling stock through every route. That will tell you what will track properly, and (more important) what won't.
Chuck (Modeling Central Japan in September, 1964)