In his review, Eric Siegal/EricsTrains strongly encouraged users NOT to use anything less than 0-72.
If you look at several of the YouTube videos of the Big Boy running, I don't see how it can possibly run on 0-60. Truthfully, 0-120ish (double 0-60) is still too tight for my taste.
And when it comes to anything UP related, accept Hot Water's words as gospel!!