Too much is written about what was the most powerful steam loco
Tests of the C&O with a dynamometer car indicating momentary readings of 7,498 hp (5.6 MW) with readings between 6,700 to 6,900 hp (5.0 to 5.1 MW) at about 45 mph (72 km/h). No one has published a higher dynamometer horsepower for any steam locomotive.