i'm 6'3" my brother is 6'5" we both had Giants which are sized S,M,L,XL They are a "compact geometry" with the sloping top tube but i'll be damned if I wasn't nearly at the bottom of the range for the XL. I would think someone 6'6 could be fit to an XL Defy, I would test ride one. Otherwise, it does make sense if you think aobut it. On any given day at 6'3 I don't typically see more than 1 or 2 people taller than me and I live in a big city, at 6'6" you are definatly in the top 1/4 percent of height. not a huge market for framebuilders