I was quite comfortable riding the train from Los Angeles to Cleveland and back as a kid - twice. But my 6'4", 250lb father couldn't handle the seats. He slept on the cushioned bench in the club car.
Later, we switched to air travel. The first time was on a 727. That sucker was LOUD!
My train-loving dad was 6’5”.
I am 5’10” woman.
I am actually shocked how spacious coach is on Amtrak.
Add to that, if your train is sparsely populated….you might go anywhere you want!
On my dad’s last trip from NE our family got on (regular train south; we had Acela north) just below Boston so it was empty, but we were heading to coach and a conductor just said, go ahead forward into our business class! It was even nicer than coach.
So things are also much more flexible on trains. Airplane, you get what you get. Likely horribly tight!