Monet, why not just email either the supplier or Mingus Dahlias and ask the height? I bet either would be glad to answer your question.

When I saw it in his garden many years ago it was about 4 feet tall.

I traded for a Mingus Nicole tuber and have it in a pot to take cuttings. The sprout has just started and when it is about 2 inches long, I will cut it off and root it in some sterile potting mix. I have wanted this one for about five years and have never seen it for less than $10.00. I am looking forward to growing it again and it is one of the prettiest large dahlias available. Tubers are notorious for rotting in storage.

Thanks, Ted, for both of your responses.
"Tubers are notorious for rotting in storage." This is the type of information I find invaluable from this forum. It tells me how to care for a "special needs" Dahlia. I will take cuttings as you did and grow it on as a pot tuber. It should store more reliably than the normal process.
BTW - I located it for $3.00 (US).