In the case of 7-letter words, almost one-third are heterograms, the fraction of isolanos decreases to about a quarter, and for the first time we have some onalosis (words in which each letter can be changed independently to make another word). Moreover, we only have to find eight related words for each ladder. These facts mean that the number of ladders starting and ending with heterograms with every letter differing between the two words, increase over a thousandfold to nearly 100,00, and more common words appear.
"Super-Ideal Seven-Letter Word Ladders,"
Word Ways: Vol. 34
, Article 14.
Available at: http://digitalcommons.butler.edu/wordways/vol34/iss1/14