Boneprone,
I have ridden an 02 Lemond Zurich for the last 5 years and I built up a Kestrel RT700 this winter. While they are both comfortable bikes in their own right, they do have appreciable differences.
The Lemond is a lot smoother because of the flex inherent in the steel frame, and while not a "touring" bike, its geometry is a tad towards that end of the spectrum, and the fork has a bit of rake, resulting in a comfy ride.
The RT has a tighter geometry, a straight fork, and is ultra-responsive. It corners on a dime, and is noticeably faster to accelerate. But because the geometry is tighter, it's not as smooth as the Lemond.
Having said that, I just completed a century on the RT last Sunday and found it to be very comfy. I'm 5' 10" and 160 lbs.
If I were contemplating a double century, I would consider riding my Lemond because of its road-smoothing nature. But I still love my RT, and ride it all the time now.