I have two tilt up monopole towers in my back yard,
One is 35 feet made with 30' of 6" and 5' of 2 1/2" with a 10' diameter Whisper H-80 on it.
The other is 30' made with 17' of 6", 8' of 5", and 5' of 4" with a Bergey XL.1 8.2' diameter.
I would not go taller without using bigger pipe, and if I did that I would do more than just add a piece of 8'' to the bottom. Total deflection is the problem and the above towers are at the limit IMO.
The bottom connection is a flange connection with a hinge pin built onto one side.
Victor Creazzi
Aerofire Windpower
www.aerofirewind.com