I run a Rail King Big Boy, a 773 Hudson, a 2321 Train Master, 15-inch 2500-type streamliners and Superliners, and 16-wheel depressed center flatcars, all on O27 curves 
A reliable O-27 layout for continuous running:
“O” gauge Lionel tubular looks like 027 tubular that took too many steroids at the gym and got out of proportion. I have several full circles of K-Line 027 profile 072 curve track. It’s now hard to find. I like it because it’s shorter in height, which gives me more to work with when a layout has multiple level. I can’t stand small 027 circles and made a point to use nothing smaller than 042 curve tracks on the last layout I built. I had probably $500-$750 into Fastrak in the yard I built around 2006 and I pulled it all up and sold it 18 months ago. Then I bought a bunch of Gargraves 202 non phantom all stainless flex track.