I've owned a Cervelo Dual (aluminum), Cervelo P3SL (aluminum), and Cervelo P4 (carbon). I cannot tell ANY differences between the ride quality of the frames.
Comfort is determined by fit and contact points (saddle, bar tape, shoes, and elbow pads).
Shimano 105 is more than enough performance unless you want electronic.
Based on your budget, buy an aero road bike such as a Cervelo S2 or Felt AR 5. If you buy last year's model, you'll have enough money left over to pick up a solid power meter such as Powertap C1 or Hed Jet race wheels.
Comfort is determined by fit and contact points (saddle, bar tape, shoes, and elbow pads).
Shimano 105 is more than enough performance unless you want electronic.
Based on your budget, buy an aero road bike such as a Cervelo S2 or Felt AR 5. If you buy last year's model, you'll have enough money left over to pick up a solid power meter such as Powertap C1 or Hed Jet race wheels.