my bike search is narrowing and I have noticed that 3 I am considering (cannondale r700, trek 1500, and specialized elite double) are all aluminum frames. Two others, the Felt F70 and Orbea Volata, appear to have aluminum frames with carbon tails. Do the carbon tails make a big difference in tride smoothness/weight. The Felt and Orbea are also appealing as they are less common. This also makes them harder to find (no lbs in my area carries either).