Conformation of peptides in aqueous solution?

[Thomas Schnibbe]

Dear Netters,

      I have a question concerning peptide conformation in aqueous solution.

It has been shown that secondary structure formation in aqueous 
solution should be negligible for all short peptides (shorter than 13 - 15 aa 
or so). 
Increased chain length moves along with secondary structure formation: Medium 
size peptides may present a population with secondary structure in a rapid 
equilibrium with random, mainly extended, conformations.
Large peptides/proteins beyond a certain chain length show stable 
(super-) secondary and tertiary structures (quite stable and somehow 
dynamic, too).

My question is:

WERE (AT WHICH SIZE) IS THE APPROXIMATE TRANSITION "DYNAMIC - STABLE"? 
                 (aqueous solution no detergents etc., room-temperature)

(Of course, secondary/tertiary structure formation strongly depends on 
physico-chemical properties of the bulk solution, the primary structure, 
temperature etc., too)

Since I'm working on synthetic peptides you would help me a lot.

Thank you for your time,

Thomas