I have been running E8A's pulling passenger cars with truck-mounted couplers around 20" radius curves and through #5+ turnouts with no problems, but if the turnouts form a crossover and creates a tightly curved "S", there can be problems. (I run mostly Athearn 72 ft. passenger cars and Con-Cor shorties, and none of them back up well around curves with the diaphragms touching.)
If you are running 85 ft. cars, passenger or freight, I would strongly suggest trying the long-shank Kaydee couplers. What you might have to do if you don't mind running one car as an idler, is to put an extended coupler pocket/draft gear on one end of a car. If you model a car that had "Cushion Coil draft gear" which extended longer than normal draft gear anyway.