My bikes followed by the number of centuries done on each in roughly chronological order:
Falcon Black Diamond: 2
Paramount P13: 4
Paramount P15: 5
Falcon San Remo: 15
Nearly all centuries were done on 27mm tires or larger, all on Brooks saddles, and most with fenders. Since organized century rides go rain or shine, fenders make an all day ride in the rain a lot more comfortable. I think tire size is a much greater determinent of ride comfort vs frame material.