It was mainly the rear...on two sets of wheels...Fulcrum Racing Zeros and Zipp 404 (admittedly not the stiffest of wheels and not designed to climb...had to swap them off my TT bike when my Fulcrums had an issue.) Have not put the 404s on the addict (and can't see a situation when I would) but I'm using very plebian Fulcrum Racing 3s on the addict right now and all is well. On the front, I would get some rub if I was really tired and using too much leverage on the bars....I'm 180cm and ride a 56 frame.

I think the chain stays on the Foil are stiffer than the addict by a small amount (And as you say, whether that is significant depends on the rider), but the top tube seems stiffer on the addict...which gives it a very planted feel.