for me it is all about "feel".
I can tell a difference in how the bike feels between the 2k and 4K versions, enough of a feeling to go the difference..
When I rode the 6K bikes, I could not tell enough of a "feel" difference to justify the money...When I ride for hours, I want the bike to feel good and I want to feel good when I am finished riding, I simply do not care what other folks think about it. I am not brand oriented and do not give a crap about the bike snobs...I have one trek, one ridley, one giant and one KHS bike....I have different bikes for different types of riding and ride the one that feels best to me.