What are differences in materials/geometry?

I see some 555's referred to as 53,55,57cm and some as S,M,L. Whats the difference?

565 has same geometry as 585 Origin and Ultra. 565 (no longer made but still available new sometimes on Ebay, etc.) has an aluminum bottom bracket shell, 585 has a carbon bottom bracket shell. As a result, 565 weights a couple of hundred grams more. There may also be a difference in carbon between 565 and 585, but I'm not sure about that.

From Look's geometry table for current model 555, S = 51, M = 53, L = 55, XL = 57.

If you're considering 555, 565, and 585 for yourself, be sure to look at and compare the geometry tables. Geometry for the 555 is a bit different from the 565/585.

I read on an Ebay ad that the 565 shared the same fork and main triangle tubes with the 585, but had the same rear stays as the 555 which is a bit heavier and stiffer than the 585. Don't know that this is true or not.

According to Veltec the bracket stiffness of a 565 is 58,1 and the 585 54,6