I would agree with Jeff.  And, add that this also depends on the manufacturer.  For example, Hilleberg (the founder of Hilleberg is over 6ft tall) makes tents that are a bit longer.  Note they make some premium tents and, they call the rain fly an outer tent and the poles attach to the outer tent.  The inner tent clips to the outer tent.

Also, the width at the shoulders can be an item to consider.  A friend of mine, 6ft+, purchased the ZPACKS Duplex (I don't recall him having issues with length) but being a bit broader in the shoulders felt there would not be enough room there for two folks and return the Duplex to purchase the Triplex.