I have a few too many glasses of wine in me but: frame material and geometry makes an enormous difference. I have a steel frame with 20.5c tires at high pressure, in many respects it's more comfortable to ride than my alum Specialized with 32c or my CF Roubaix at 25c. I'll opine it has to do with the frequency/wave of the vibration and the intensity when it gets to your bones. On the CF bike is has a delayed reaction, that deadened THUD, which I just don't like. On the alum bike its more of a long snap that radiates through-out the frame, even with larger tires. On the steel bike it has a fast, mellow, single jolt and then it's gone. On a long ride on bad roads, I'd take the steel bike and narrow tires. Except for the weight penalty, cr-mo steel / relaxed geometry is the plush ride, hi-ten even more so ....regardless of tire size.

Cr-mo frame and hi-ten fork -> budda ride.