There's fast trains. There's big trains. To be pretty big AND fast is a defining position. Movin' like a freight train is to be an unstoppable force, taking all the bumps, be a perfectly oiled machine that won't ever quit. This is the UP-844. It weighs 500,000 pounds by itself. It's doing 75mph. (on 80 inch wheels for scale) The only car I've ever been in that was close to feeling like this was my dad's old W126 Mercedes 300 turbo-diesel set at 80mph....and I'm sure it wasn't even close.
Below is a slightly slower, but much bigger version of the true freight train concept. The Challenger. Only moving at 60mph or so but it weighs twice as much. A million pounds. (The main wheels are 69 inches tall-for scale, it was built for torque pulling miles of coal cars.)
About four more years to go and the big-boy will be out of restoration. I plan to go watch that one on it's big post-restoration tour.
These aren't the fastest. They're just the most impressive demonstration of the concept.