maybe. if the carbon is stiffer, it probably accelerates faster, and that might be noticeable...but it won't change your avg speed much over the course of the ride.

i haven't ridden Ti (or a nice steel road bike for that matter), but i would guess road feel also has something to do with it. don't steel and Ti have a softer ride than carbon? that might make them feel a little less quick and snappy...don't really know, just speculating.