So I was running trains, and trying some switching on my little 4x10 layout, which emphasized what I already knew: its pretty darn hard to couple on a curve! I took a look to see if I could increase the diameter of the yard tracks. With a couple of adjustments, I was able to go to O108, O99, O90, O81. I think I may order some of these wide diameter tracks to see if coupling can be acheived, and under what circumstances.
About 73.5" on the longest yard spur. The three in-most yard tracks all have straight sections of track before the curve, which will help with coupling a cut of cars on the straight, which may then extend across the curves to the end of the spur, and the coupling can be achieved on the straight sections.