Originally Posted by Garfield Cat
Consider this: Cervelo has the sloping top tube in its road racing bikes. More riders will say that's the way to go if you want to race. Cervelo also makes time trial bikes and their top end bikes are not sloping.
That's because TTs and Tris usually have the rider in a seated position more than in road racing as power is generated. A traditional, non-sloping, top tube provides less flex on the seat tube, which helps. Also a long seat post may not be as stiff or strong as the seat tube.