Well, classic steel like the Panasonic, not modern oversized diameters. Classic steel diameters ride pretty mellow and nice compared to oversized aluminum like a Concept or Argon18, but of course there's many factors affecting ride quality, most importantly the wheelset...

The geometry on the Concept is steeeep, like 75 ST/74 HT on a 55cm. I don't think it'd be much fun for long rides, I certainly don't plan on doing any on mine once it gets built. I didn't understand what you said by Concepts don't like to be locked up until I flicked the tubing with my fingers and saw firsthand how thin it really is.