it is a balance between comfort, flexibilty and aerodynamics and depends somewhat on what type of riding you are doing.

I find for me, and I do long distance riding (4 to 6 hours), that comfort allows me to ride further, faster than great aerodynamis. I have my bars about 1 cm below my saddle and can ride in the drops all day if need be. In other words, I can get aero but still be comfortable.

As to the bike you posted. I had a 5500 and can tell you that Trek's geometry is (for most riders) conducive to either large drops, many spacers, riser stems or some combination thereof, compared to other geometries. Treks, seattubes are approx. 4 cm shorter than their TT when measured center to center. This means that, compared to a regular "Square" (56 X 56) frame, a Trek frame will have 4 cm of additional drop or spacers or spacers and rise etc, to get the bars into the same position. Just a thought.

Len