Per my experience, I'll definitely suggest that you consider a good carbon frame. I have owned and ridden steel and aluminum frames (CAAD8), but none of them compares to the Lemond Buenos Aires I currently ride. And I have ridden the CAAD8 and the carbon bike with the same wheelsets, tires and tire pressures.

The carbon just does not beat me up as much. I can ride my typical 70milers two days in a row and still feel not beaten-up, which I couldn't do on my CAAD8 frame. YMMV.