What is the weight difference between frame sizes?
According to the Weight Weenies.com web site listed weight can differ from actual weight by as much as 10-13%. One thing you should be aware of is there is some variations between identical frames due to manufacturing  tolerances. Most weights listed in advertising literature are not for large frame sizes. Looking at the listings on the site it appears that a 20-40 gram difference between carbon frame sizes is about the average.