India is running non-well doublestacks under catenary at mainline speed. To be clear, their double stacks aren't even the well cars we use, they're standard height flatcars, with two containers stacked on top, running under 25kV catenary. https://www.youtube.com/watch?v=zmNbqGp6KXU This video here looks to be 40-50mph and sources I can find say they'll be running up to 62mph (100km). I admit, they are using 5'6" broad gauge and not standard gauge, but since we use well cars, I imagine the reduced height needed for clearance over here would make up for any reduced stability. But given this, I don't see why a passenger unit couldn't run under double stack-clearance catenary at shared speeds (up to 80mph), with lower catenary on passenger-only higher speed portions. Any at-grade crossings (like I'm sure you'd have in VA and NC) would be slower speed anyways.