I am looking to buy a LOOK 596 tri frame set, however I am very much in doubt of sizing. Unfvortunately, I will not be able to try before buying, and therefore it is kind of important that I get it right. Reading on this forum, I can understand that the Medium comes out in a kind of “tall and short” (which I prefer) compared to the L and S. I am 185cm tall, legs 88cm. Can anybody throw a piece of advice concerning sizing? (I used to ride a 56cm Transition and an old Zipp 2001, large frame, small beam).
Take a look at this resource:
http://www.bikesportmichigan.com/reviews/Look_596-2009.shtml
Including this information on sizing:
Size names for the Look 596 sound smaller than they actually are and will likely confuse many customers. The bikes run very large making the size names sound absurdly small. I tested both the extra small and the small sizes, ultimately settling on a “small” which fits roughly the same as a 54cm Cervelo P3C. I’m 5’9” tall with a longish torso. The idea of riding anything called “extra small” just didn’t sound right- but it would fit me well using the longer stem. The real difference between “small” and “extra small” is the length of the top tube- they have the same head tube and seat tube center-to-center measurement. The Look 596 will not fit smaller riders. If you are less than 5’6” tall you can cross the Look 596 off your list- it won’t fit. The extra small and small frame sizes measure identically in stand over height, seat tube length center to top (not counting the extension above the top tube) and head tube height. The only real difference between the small and extra small is effective reach or top tube length. I have a longish torso so I went with the “small”. Better names for these two sizes might be “small regular” and “small long”. Whatever the case the geometry offers some unique sizing capabilities especially in terms of reach dimension- it’s just difficult to figure them out based on some rather ambiguous size names alone. 
Size names on the 596 don’t offer much information but their geometry charts give accurate dimensions except for forward seat angles.
Look’s geometry chart for the 596 is not very useful for steep seat angle riders as it does not depict the bike in the more forward, steeper seat angle configuration. The effective seat tube angle on my bike is 79 degrees, the same as my Cervelo P3C. I’m looking forward to Dan Empfield posting stack and reach fit coordinates for the Look 596 on his Slowtwitch website for a more accurate comparison to other bike fits. Prior to Empfield’s examination I would suggest the bike runs high, but with size names sounding utterly out of whack. Few riders at 5’10” will relish the idea of being on a frame size named “small” but most in that height range will fit that size name.