Donald, my 'Sears Tower' has been in a 2-3 gallon pot for several years
, and it has never approached its registered height of 72" (6 feet). The height of the pot is maybe 10" or so, I am 5' 2", and I see the blooms pretty much eye-to-eye, so that would give it a height of 5' 4" at best. Of course, that spot in the garden does get a lot of shade, so that might factor into it.
My husband is 6' 3"; here is a picture of him with the (potted) 'Sears Tower':
edited to add:
I forgot to say that once 'Sears Tower' gets into bloom, I have always had to stake it as the scapes leaned and flopped. I don't know if it is because it is grown in a lot of shade, or if it behaves like that in full sun situations. So depending on how you support the scapes, the blooms would be at a lesser height, still.