This is my first time on this thread and I would like to provide some feedback as a, about to be, first time SNS owner (current AW13 styles).
Let me preface by saying I am 5'10" and 170.
I ordered the ION in size L and it appears to fit well.
I have had nothing but grief with the STARK. Size L was too tight - size XL still seems on the slim side. When I compare the sleeves on the XL Stark with those of a L Ion the Stark sleeves are 1/2 the width !!! I cannot stand tight sleeves on a wool sweater.
I now have an XXL coming in the Stark. According to the Mr. Porter website there really is not much difference in the length of the back or sleeves on any of the Starks. Size L is 25 long - the same length as the XXL. The shoulder is 16 on the L while only 17 on the XXL. The sleeve length on the L and XL are the same at 30.5 while the XL is 32. To be honest there really does not seem to be that much a difference between the L, XL, and XXL at all - at least according to Mr. Porters measurements.
Do Starks stretch out and become less tight? Is it a negligible stretch or is it noticeable?