It may seem that a 5-square could contain nothing but familiar words, but these 5-squares have eight words which have to fit, of which at least one must be a reversible word, and at least one a palindrome. In the case of six-squares, there was just one square with as many as 7 words (two less than the maximum) among the most used 87,000 words: in the case of five-squares, 3 squares had all 8 words in the top 87,000 (and 66 squares had just 7 words).
"All-Diagonal 5-Squares With Simpler Words,"
Word Ways: Vol. 39
, Article 12.
Available at: http://digitalcommons.butler.edu/wordways/vol39/iss4/12