If you're using numbered turnouts (#5/11-degree, #6, #8) you probably don't want to use cut-down sectional curves to return-to-parallel. You'll get a better look just using flex track. Be prepared, though, to use the length of the straight segment of the turnout to make the curve. See the illustration below:
From top to bottom: #4, #5 (11-degree), #6, #8, and #10 Ross turnouts. The straight section following the turnout is equivalent to the length of the straight leg of the turnout. Spacing is 4 inches.
According to Ross, the point radius on the #4 is 36" (O-72) to handle larger equipment. NMRA specs say it should be 33" radius (O-66) Tests with my scale-wheeled Big Boy indicate it won't work with large-wheelbase scale-wheel steam. The #5's handle my Big Boy and my scale-wheeled Hudson fine.
As you go to the #6 and beyond, the frog gap gets larger and will not support scale wheels without modification of the frog. We put a moving point in the frog on the #8 curved turnout on the club layout.
