A: The smaller radius of O-27 track precludes running longer consists because the locomotive will pull the cars through the curve and cause a derailment. Also, the O-27 track is less rigid than the O gauge and can get out of alignment.
I think you should decide on the trains you enjoy running and then determine if they’ll run on O-27 track. The longer aluminum passenger cars will hang over on the curves, as will the longer steam engines like the Hudsons and diesel locomotives such as the Fairbanks-Morse Train Masters. Some locomotives like Lionel Berkshires, Scale Hudsons, and Train Masters won’t clear O-27 switches. O gauge track will provide you the flexibility to run almost any Lionel train from any era.