Ditto, I agree. The weight won't make that much of a difference. But going from 1.5" tires to 23c tires (or 28c tires or whatever) definitely would. Not to mention significantly lighter wheels, although that's more debatable.

Also, a road bike might put you in a more aggressive position that would allow you use slightly different muscles to go fast, if that's your thing. I could ride my touring bike practically forever, but I could never even come close to sprinting on it. On my road bike I can go much faster - BUT for much shorter periods of time. It seems to allow me to exhaust myself, whereas my touring bike didn't...just a tradeoff.

I don't know about the "more aerodynamic positition", though. Touring bike have drop bars - I really don't think it's made a difference unless I'm going like 25mph, and even then it's negligible.

Back to the original post, I went from a touring bike that was a little to big for me to a high end full carbon road bike (a Specialized Tarmac SWorks SL). It "feels" faster, but I don't go that much faster - probably about 4mph, and that could be attributed to skinnier tires. I don't regret my purchase, as I find it *much* more comfortable, plus it's much better at accelerating. But I was suprised there wasn't more of a difference in speed.