as you move up the shimano line you find the price increases quickly because of the man hours involved in manufacturing the product. a 105 group has more man hours than a tiagra, a ultegra has more than a 105. I'm sure you get the picture. basically ,the tiagra stuff is tossed out rapidy by a machine and gets very little inspections compared to a da20 or a ultegra . which is the best? simple, the dura ace. by how much? maybe 1percent , maybe 2percent. maybe you will shave 3 minutes off you p.b. in a hundred mile race. you wont notice squat over short distance OVERALL. I'M NOT TALKING ERGONOMICS HERE . Research and development is slow, expensive and so is paying people to measure bearings with a micrometers .so there is where your extra money goes. Its just a hell of a lot cheaper to rapidly machine produce equipment with no human contact. i say go middle of the road, 105