My brand new G5 thats new new already had 8 hours and 150 miles on it, right out of the box at the hobbyshop. compared to the 10 minutes and 5 miles it would usually have.
I seen 850 plus hours and upwards of 40,000 scale miles on some engines.
These engines were at a model train museum, but privately owned. The owner runs them when hes there alot since he has no layout, and when he is away, (he drives a semi) i take care of the maintance on them. The engines would run about 6 hours a day, about 6 days a week. They normally ran at about 20 miles an hour. In the year or two they still run, but would need a rebuild.