So I looked it up, sir; that web-site has a lot of information on it. Apparently the "Big Boys" are considered the "largest," because they were the largest in general standard customary use (during the 1940s and 1950s), while the other ostensibly larger ones were one-of-a-kind models and try-outs.
I hate to tell you what came up when I tried Googling this; the sites gave nowhere the information the site you recommended did.