Scott T,
As far as I know the tanks on the MTH flatcars are made by Hobby Master and are 1/48 scale. Corgi tanks are 1/50. I have both on my military train and you can hardly tell the difference.
Did MTH put a single Sherman tank on a 50' flatcar as well as a 41' flatcar? I have 50' flats with 2 Sherman tanks but the last two cars I bought only had 1 Sherman but the car was longer than a 41' car.
Thanks
JohnB