@Will Wilkin - Welcome to the forum - I have 2 MTH Premier crocodile locos. One is high rail, one is scale wheels, both supposedly will take 072 curves. The high rail engine runs fine, the scale wheel engine derails as soon as the curve comes into play. (Both run fine going straight.) This is on Ross track. If you forget about running anything with scale wheels, you should be fine, they will take the curves without derailing, but whether they look good is another matter.
One of the things I have learned, is the issue of track radius and diameter and then type of track. O-gauge can refer to semi-scale and scale, but within scale you have high rail (3 rail / 2 rail) [HR] and 2 rail scale [2RS]. Reading the replies I think everyone is assuming you are thinking high rail. As with HO, the 2 rail scale enthusiasts talk in curve radius. High rail enthusiasts talk diameter. HR runs fine on 072 dia, but I think you will find 2RS needs much bigger curves approaching 120 inch diameters - depending of course on the size of the engines. You could have seen articles from either camp. HR engines can run on just about any type of track, 2RS ideally has solid rail and a flat top surface (no traction wheels for these folk, heresy). In addition 2RS wheels are intolerant of less than perfect track laying and most likely lower quality switches. Lastly, some of the "look" issue is driven by the length of passenger cars. 21 inches, 19 inches and 12 to 15 inches. I think most high railers would agree that the 21 inch cars (which can be stunning) do not look that great on an 072 curve. Mostly due to the middle of the car body overhanging the inside of the curve.
Its your railroad, you can do what looks good to you.
