Great photo of you Gil .... and a great shot of a fantastic locomotive!
There is a reference I'll link here, that may help some folks come to better terms with these monster steam locomotives. The bigger articulated locos (two engines hinged under one boiler) are listed in the lower half of the page, while the explanation as to the place the Big Boy fits into this Pantheon of power, is near the bottom.
Enjoy:
http://www.steamlocomotive.com/misc/largest.php