I have both Eastern Kings and Black Milks. My eastern Kings are about the same length as my black milks (around 5 feet), but are slightly heavier bodied.
Realize that 7 foot black milks are not common. Most seem to get to around 5.5 feet for females and 6 feet for males.
If you want big colubrids, the obvious choice would be an Indigo or Cribo. A 6 foot cribo is a MUCH larger snake than a 6 foot kingsnake.
For that matter, most bullsnakes/pinesnakes are larger than kingsnakes as well, although they aren't as gigantic as Indigos.
There are also some larger old world species.
Some of the species of Ptyas get over 12 feet.
Some of the Beauty Snakes readily get to 8 feet, and they grow like weeds!
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Chris Harrison