I have owned the Trek 2100 Composite, Giant Cadex 980c, Specialized Epic Sworks Carbon mountain bike, and a Miyata Carbotech mountain bike (still have this one). I have not found much of a difference in ride quality between steel and the carbon models I owned.
I did ride a Miyata Team Carbon several times and a Miyata Team Titanium once along with a 100 year anniversary model. The Team Titanium was a very soft and flexible ride when compared to the others or steel. That bike opened my eyes to frame flex and how much I really do like a flexible frame.
As far as I know all the Miyata carbon road bikes shared the same main tubes. Rear triangles may had held some differences in chain stay length, but nothing else other than components after that.